The Blight is not "an illusion", it's a different reality held together by an energy foreign to Creation. This energy prevents the Wheel from reverting things to normal.

The Pattern, ie: reality, is woven of saidar and saidin (of which there is a finite quantity). The Blight is part of a twisting of reality by Shai'tan (quite literally, since he is the True Power, which strongly suggests its counterpart the Creator is similary the OP, and thus Creation is also the Creator). It is corruption, reality is altered, and these alterations are cause to effects (the distortion of the weather, for example, or the altered nature of plants in the Blight etc.).

When Shai'tan releases or loosens its grip, by the evidence in EOTW, reality in the Blight reverts to its normal state and quite fast. Without an opposing force, the rules of reality rapidly reassert themselves (maybe even in a blink).

A fundamental difference between the Bore/SG/the Blight and tel'aran'rhiod is that reality in TAR is just a reflection (held together by eveything that has a thread in the Pattern, it seems to me - thus the "shiftings" when the inconscious of a soul visualize a specific detail - the room with a door closed, while another inconsciou visualize it open. A little girl's inconscious visualize her doll on the floor, no one else in the home has "recorded" the doll (except mommy, who of course visualizes it on the shelf where it should be, not where the little one left it last). The more permanent/old a feature, the stronger the collective inconscious is holding it in place. It normally won't snow in summer in TAR, but on occasion it might, if enough souls are inconsciously visualizing a snowstorm at the same time... say the night in summer when Cenn Buie told the assembled village stories about the snowstorm of the century.. that night, it might snow in the TR reflection in TAR because enough people dream of snow) and can be shaped by the mind of a Dreamer (conscious, thus momentarily stronger than the collective inconscious), while the DO's corruption isn't primarly a matter of will, it's above all a matter of power/energy. The corruption is fairly limited. The further away from the Bore, the less reality is affected, and time and distances are unaffected, and so is the basic shape of geography, at least away from SG. Lifeforms (flora, fauna) are the most affected. The DO needs the True Power to reshape reality to its will. A tangible proof of that is how the weather patterns were altered by Shai'tan (probably starting the chain reaction from the area of SG), and how a great enough effort with the OP to fight this off was sucessful. Shai'tan did not have enough power available (within Creation) to struggle and overcome the effects of the BOtW, and before the Bowl was used, it appeared the Wheel was incapable of correcting the weather patterns directly (micro-management of the wheather is probably not part of its programming). The OP won that round, it wasn't a fight between wills, as would happen in TAR. Similarly, the Wheel doesn't seem to have enough available "free" energy to totally overcome the Blight. It manages to keep it from advancing, but unless Shai'tan retreats (as it apparently did in EOTW), the Wheel had to give up on a whole circle around the Bore, where Shai'tan's power is just to strong too be completely negated. The Wheel appears to focus on preserving life. It held the Blight above Malkier, but when Malkier fell and the Malkieri retreated, the Wheel seemed to have "given up" on holding off Shai'tan's advance over the area. I don't think there's anything Dreamers (or channellers, for that matter) can do about that (though I have this idea that possibly Dreamers - incl. wolves - might be able to help in the special conditions created by the sounding of the Horn, when TAR and the real world seem folded in a special way. This is why I think Rand must open his side and die, using the shock of the Taint of SL and the TP mixing (a cataclysm similar to what happen at SL, except worse) to make Shai'tan momentarily lose his grip and retreat into his "prison", then the Horn will be sounded to bring Rand back for the other step of the job... take advantage of Shai'tan's retreat to reshape reality without a Bore. This would require Perrin and Mat being "one" with Rand, acting in perfect coordination - a single will - through their mental link.. and my pet theory is that Egwene has to die at Rand's side at TG, and will turn out to be another Hero of the Horn (some sort of Moon Goddess/heroin, counterpart to Rand, the solar hero). Perrin will provide her "interface" to the dreaming wolves. Egwene will "hold off" Shai'tan (by denying the reality of the Bore, while TAR and the RL are folded together by the Horn) while Rand seals the Bore without TP interference, thus removing the weakness. Or something like that....).

TAR vs. the DO is very much an unknown. If we remove Slayer and the Forsaken (dreamwalkers especially) from the equation, there's nothing tangible so far to suggests the Dark One has any power over tel'aran'rhiod, let alone that his powers are greater there than elsewhere (if anything, it appears to be the opposite, ie: TAR is unaffected by the DO, perhaps because he can't be bothered to expand energy over a dimension which is just a reflection, or perhaps because he would need to fight the collective inconscious constantly to affect TAR permanently) TAR appears as unsullied as ever. The corruption of the weather does not show up as much (in a few scenes, not at all), and the twisting of the area of the Blight (a reality that possibly exists to the Wheel not as "reality" but only as a foreign energy - the distortions of the TP there aren't part of the Pattern) seemingly results in an incorrect reflection that makes the area impossible to enter via tel'aran'rhiod (TAR would reflect the distortion of the pattern there, but not the layer of TP-created reality over it. In short, nobody knows what the Blight in TAR looks like (it's not the Blight as in the real world, nor the area as it would be without Shai'tan), so you can't visualize it to enter it. The exception might be Ishamael's palace, because Moridin lives there and like everyone else is connected to TAR and his inconscious may "record" this location and thus it is reflected in TAR). There may also be an area outside SG (at a safe distance from Shai'tan) and including Ishamael's place, which Shai'tan leaves untouched on purpose. It could be the only place in the area where not only you can enter from TAR, but also the only area you can Travel to and from (I get the feeling the distortion of reality makes Travelling in the Blight impossible).

As for the global vs. localized nature of the Bore, I always understood it this way: time and space are constants of reality, inescapable rules within Creation, but do not exist outside of it. The Bore is a global weakening of the barrier between Creation and Shai'tan (similar to a material only 95% impermeable - the liquid outside would mix with the liquid inside, at a very slow rate), and Shai'tan seeps through it globally, there is no when or where from its side of things, but the instant the TP crosses the barrier, this phenomenon manifests itself in space/time within Creation. Until/Unless he is powerful enough to overcome the rules of reality (and/or the system has become so chaotic inside that the whole system unravels), Shai'tan is bound by rules such as space and time (and everything else, down to how the rules of the weather) for everything he does within Creation.

We do not know for sure that the Bore (localized etc.) exists in all the worlds. What we know is that it exists in all the Mirror Worlds. We have yet to find out if there is a Bore in the realms of the Aelfinn and Eelfinn, or if the global weakness of the Pattern has affected these worlds differently, because the rules of reality are slightly different in these dimensions.