There was absolutely nothing wrong with 26″ wheels but a lot of gullible people fell for the marketing BS, which dragged the MTB scene in that direction.
Yes.
And No.
I’ve a few mates that were 26er die-hards. Then got bikes with bigger wheels and realised how much better they were. Not gullible people mind, but people who know how to ride a bike, and what they want from it.
Myself, I had a 27.5 but ended up selling it to create some cash to buy my gravel bike. But have two 26er MTBs to do MTB duties. The Inbred SS I really enjoy riding. It’s brilliant actually in a very simple way. The 26er FS I don’t get along so well with, and certainly, whilst it is a more capable bike than I am a rider, I increasingly feel ‘disadvantaged’ compared to mates who have bigger wheels and, at least as importantly, more modern geometry.
So, not having tried a 29er, I can’t speak directly from personal experience, but reckon the big wheel debate has pretty much been won, albeit modern geometry also being a key factor.