Regardless of size the same challenges will present themselves. Encounter spaces will still be made significantly easier to Navigate with a Warlock. Damage checks will still be easier to manage with certain specs. The buff/debuff matrix is still something that is a gain to manage effectively.
The 20man size made it so that these challenges could be made with some roster flexibility after the fact all of these checks have been made.
However, challenges that some guilds face are purely down to the management of a guild and the raid roster. This isn’t an issue of the game per se but one that can be resolved by making those challenges easier to navigate.
For example, a second gateway option could be afforded to mages as a “mass blink”, debuffs could be given out via consumables at a weaker rate, buffs could be done via consumables at a weaker rate (as they had been done in the past).
For the final stage of the number of people. To be honest, that’s not an issue. If you’re wanting to push to the highest levels of the game, some level of organisation is required on your part, if that’s not for you then you jump ship to find a team that’s willing to do that.
Finding a team where the goals resonate with yours is your prerogative as a player. Yelling into the void isn’t going to fix that issue.