We gotta remember that this series was supposed to be much shorter. Since all of the Chosen were "good" at some point, important people and pillars of the community, their flaws are well-remembered. This also highlights their respective personalities, and why they'd sell out *the whole world* for power. In a 3-4 book series, you don't need to do a lot more with the persona of 13 big bads.
Sadly, Jordan gives us far less info than we'd like on the Age of Legends - the time, the people, its technology. For him, the focus of the series was the present time and a small set of characters, most of whom were from a tiny village.
He said the origin of the book was partly homage to JRR Tolkien, to establish a point from which his adventure would diverge. Since the series became massive, he couldn't leave the 2nd tier villains out altogether, could he? But he either didn't find them necessary or interesting often enough to really give some of us what we wanted from them.
I think this makes a lot more sense given how the series expanded. RJ apparently set the series length at 3, then 4, then 6 before it became ?? And in those matters, Jordan is skilled and thoughtful, and worked hard at his profession. So I can't chastise the good author, even if I wish things were a little different (or perhaps more clear?).

Also, I'm pretty sure that our heroes haven't really been in the hands of the FS very often. Gloating is a villain thing - a minute and a half of it is a problem, but ten seconds makes sense.
Considering moments that could've led to a major Lightside death: Belal's calendar must've been too busy for him to meet the Wonder Girls right away; he tried to get Rand to release Calandoor before killing him. Semi didn't know who Mat was, and BalthaGar tried to channel him to death, but he was somehow completely protected! Ishy plays games with Rand twice, then goes for the throat right away - "when I'm done with my evil speech I will TAKE YOUR SOUL." And then he started to. The Gar's V1.0 were fresh out of their prison and rather messed up. Lanfear is a naughty girl and she wants her dreamboat. Moggy played the spy game in a Tanchico hotel before she fought Nynaeve to a standstill - after nearly getting vaporized, Moggy ran.