That's complete BS. Jordan had already started the "wrap up" phase of the series with KOD, in which book he placed everything he'd need for the first act of the (long planned) finale. He started giving his explanation that the rest of the story really ought to be told in a single book before he even got diagnosed.

You also peddle the absurd notion that Jordan was stretching it out on purpose (and that wasn't a storytelling choice but money grabbing). The facts don't support you there either. Jordan was entering a phase in the development of his next series that made him eager to get to that, beside his project of a post-WOT trilogy involving Mat/Tuon. He's the one who put an end to Tor's idea of publishing a short novel in the year between the main books, to which he had originally agreed and signed a contract for. He later chose not to write the second and third novels to focus on the final WOT book (and yes, that all happened before he got sick) - postponing them almost indefinitely as he began to say he' might prefer to write the Mat-Tuon trilogy after the first book of IoH as to him they'd be much more interesting books to write as they'd be more complex (Jordan just didn't like the short form, focussed on just a few characters).

As for how the series got longer, Jordan explained it well around the time of book 6. When he outlined the series to sell it to Tom Doherty, he envisionned a trilogy - he had the start (which became books 1-2-3, and the end, AMOL, mapped out. In a large part, he worked backward to outline WOT, having conceived how it ended and figuring out how to get to the beginning). Doherty told him right away he couldn't see how Jordan could fit the story he was describing in three books and signed it for six, with a clause giving Tor first option if it got longer. As he wrote, Jordan was first forced to split his first book into three. His intent, as he explained, was always to give the books the feel of an historical saga. He had underestimated how much details he would have to go into to get the tone/style he wanted, because in a made-up universe you can't count of the readers' historical backgrounds to fill the holes. Jordan has commented it's around books 4-5 he really got the tone/pacing he was aiming for.

The other lengthening, towards book 8-9-10 he never commented on, though it obviously comes from increasing problems with his outline where his plans for the finale were very set in stone and depended on the characters reaching specific points all in tune (WH is the book that caused the big problem, instead of advancing the other storylines to keep up with Rand, Jordan focussed on Rand to reach a big clima. Unlike Martin, who took five years to solve similar problems, Jordan kept going and didn't manage to get himself out of his structural problems before KOD, which took a few shortcuts (the Egwene c?apter where she summarizes all her captivity, notably) and put things back on track.

Jordan saw issues with splitting AMOL. After BS did, it's rather obvious why. The story isn't structured to be split in three books. Brandon managed it by stacking together all the material for acts 1-2 for the two big storylines, leaving him with the mess he made of TOM.

Another thing to factor in is the marked differences in storytelling styles between Jordan and Sanderson. Jordan's prose was more florid, more detailed, but he was more economical. Jordan wasn't conventionally slow paced. Even in some of the later books a storyline could consist of a few chapters only, with many ellipses The story advanced slowly because Jordan had too many storylines to juggle in one novel. Typically the Jordan chapters would involve many secondary characters that came in and out to "place things" briefly that would resurface later in the book (or the next...). A background detail, an allusion to this or that that allowed Jordan to make tons of ellipses. Jordan has very rarely needed Romanda/Lelaine scenes (and we got but few Elaida scenes, for instance). It's stories he developped mostly through allusions and brief apparitions woven in other POVs.

Sanderson is a far more linear/one-purpose writer, in part because he just doesn't "possess" the series the way Jordan did, in part because Jordan probably didn't wove together all these allusions in his notes but rather while writing - and Sanderson rather try to follow the notes/outline (where for instance what goes on with Lelaine/Romanda is told, not just the moments Jordan would then decide to show in the background).

Most of his WOT scenes serve but a single purpose or two, and he usually didn't make many ellipses à la Jordan either. Sanderson has a great deal more scenes than Jordan would have there, and they are only relatively shorter. Jordan would never have spent (about) four chapters setting up Aviendha's departure, through very redundant POVs. He would have given us ONE Aviendha POV, probably the last one that revealed what was going on. Jordan would have shown something was up with Aviendha and the WO by having Rand, Min, Cadsuane comment on her in their scenes. Combined with Sanderson's attempts at being descriptive in the Jordan style, this makes the finale in Sanderson's hands significantly longer than it would have been in Jordan's hands. With Jordan, we would have been on-screen witness of far less moments, but those we saw we would have in greater details.

Actually, this is present in TGS but it's really in TOM Sanderson's "bloating" showed the most, probably because it started appearing not in secondary scenes but even in the main storylines (it's terribly obvious Jordan intended to deal with Perrin in particular in far less chapters, but no doubt Mat too. It's Rand and Egwene who needed more space in acts 1-2 of the finale).

Had he lived, I think Jordan would probably have insisted to the end to write AMOL as one book even when he realised along the way there was no way to publish it as one book. He was very aware of the structural problems splitting it would cause (that's the reason he's given not to split the finale.. something Harriet/Tor/Sanderson chose to ignore to their grief), so my opinion is that he would not have tried to split it, he would have finished all of it and insisted it's published as volumes, together or apart over a few months. My bet is that there would have been not three of them - Sanderson has shown with the result how little sense that made to split the book this way - but two, a very fat one comprising the events of acts 1-2 (TGS/TOM) and a shorter one with act 3.