The 10 man guild I was in merged into a successful 25 man guild during ToT so I have lots of experience with both sides of this argument.
When I was a 10 man guild I thought the loot situation was bad.
It is a statistical fact that because of the small sample size of gear that is dropped (2 items per 20 compared to 6 items per 20), it is less likely that after short period of time a guild of both raid sizes will get a certain drop. However, after a
long period of time you would see that both 10 and 25 man guilds would have the same
particular-item-per-person drop rates. And this sucks. It sucks that in a 10 man guild I would be less likely to receive the Immersues Amp trinket quickly than I would do in a 25 man guild. I don't want to have to wait a long time to see it drop.
Since moving to a 25 man guild I haven't geared up any quicker and funnily enough it feels easier to cope with. You can just feel that you are less prone to bad RNG however
it still does happen in a 25 man guild even if it is less often. Conversely, it's more likely that a 10 man guild will have the perfect item drops than a 25 man guild would have so similiarly, a 25 man guild is less prone to good RNG too.
In a 25 man guild you're usually waiting for your 'turn' to receive an item whereas in a 10 man guild you're usually waiting for it to actually drop, these two waiting times are on average the same unless of course are your guild's star player and you get given gear relatively quickly (or you play a lock
)!
The argument that 25 man guilds have a higher iLvl therefore the loot situation is better is a mute point in my opinion. Whilst 25 man guilds do generally have a higher iLvl, this is because of the different warforged rates which I think (read: assume) that 25 man is tuned for anyway.
A lot of people are saying tier bosses should drop 2 items + 1 tier piece and that this would solve a lot of the 10 man loot issues and I agree to an extent. I believe to make this fair you would need to make 25 man tier bosses drop 4 items + 3 tiers pieces. A 10 man guild would benefit more from this change than a 25 man guild.
This is intentional. The idea is to make 25 man raids more attractive and rewarding as maintaining a 25 man guild is harder than maintaining a 10 man guild (this is Blizzard's opinion, not mine).