It's more based around the very tippy top teams finding success with larger hero pools. Like the transition is happening. The last podcast Monte and DoA did talked about it some. Teams like EnVyUs, Cloud9, LW Blue, Lunatic Hai, Misfits, etc. have had their rosters tuned more towards flexibility lately and have shown easy adaptability in matches. There are still gaps in these teams obviously, but it is definitely the way the pro scene is heading.
I think it's just impractical to have these small hero pools when making rosters or when adjustments need to happen. Again, whenever EnVyUs had roster issues they could just shuffle people around and add Mickey because everybody on that team is mad diverse. Yeah, they lack Genji/Pharah atm, but even then Taimou, Harry, and even Mickey are working on picking up that slack. It's the same thing for teams that can switch around every time a patch drops.
I think the ideal team atm is just have 3~ peeps that can flex most off tanks and DPS, A support that can flex all the main supports, a Lucio that can flex off Lucio into tank/DPS at least in a limited way, and a dedicated Rein that at least can flex to anything in the tank category.
Whenever Lucio/Rein become not required I wanna see who is actually good in the pro scene and who just happened to be in the right hero position. I know for a fact there are players on those heroes in pro teams that might not survive that transition.