This this this this this.

People should ideally be raiding because they like the experience of raiding. If you prefer 10s, raid 10s. If you prefer 25s, raid 25s.

Unfortunately loot lust gets the better of people and their preferences fly out the window when they can get equivalent loot "easier". This is proved whenever this topic is raised and plenty of people say that they prefer 25 man raiding over 10 man, but they have to raid 10 man because it is easier (and let's all conveniently pretend T11 didn't happen if we're trying to "win" this argument).

The problem in this expansion has been the complete failure on Blizzard's part to balance the raid sizes equally so 25s are dying a painful death. If the raids were truly balanced then this wouldn't be a problem, at all! People who want to raid 25s can do so without feeling like they're being punished.

I feel the organisational argument is flawed. You have your core raid roster, and you have backups for X number of slots. If you run the risk of not filling your 25 roster... have more backups. Yes that is a simplification, but that is all it really needs to come down to. And if you really can't get 25 on one night... well Z got it right above with the comment on lockouts. Killing an heroic boss in 25 or 10 should not lock you out of the other size. And if the 2 raid sizes were equally balanced then there would be no need to anyway.

As for how to balance them... I have no idea. But then I don't have decades of experience in encounter design and also don't get paid (presumabely) quite lucratively to do so.