I don't think having guild experience is the main reason why people are having a problem with 25s. It's more likely the logistical issue of having to need 25 people on and having that conflict with who gets in and who doesn't.
If you have a guild big enough to do 10 or 15 mans, and suddenly you need 25 the next week, it means you'll have to recruit outside your guild for that week only. You'll see the same problem that Karazhan drama caused at BC. People running two or three groups of kharazan, and then you had the a group, the b group, and if lucky the c group.
The C group gets bitter they can't beat the bosses, and even when they did start doing 25s, they were more likely to be the least geared, and be least invited to the 25s, which would cause them to be even less likely to be invited. Which just started an ugly chain.
See with 25 mans being exclusive to each week. Its not like a 25 or 10 man difference for raids. It's literally, am I going to be bging this week or not. We can't suddenly play 10 man AV and still get our points that way. If we don't have the people, it just means people will be skipping altogether. Though people wouldn't be getting guild experience, that would be the least of their worries.
Larger guilds will get experience faster, that's just going to be a fact the way the system is set up lol. I don't think you'll need to worry about pvp experience hampering down on that. Sounds to me more like someone who just wants to race to the top level and insecure about other people that don't affect them. It's not like you wouldn't be able to do, gasp twice as many 10 man bgs as a 10 man guild and get experience that way? Or maybe thats just bizzaro logic.
Personally, I'm glad that they removed 25 mans. Having to need to field that many people would be a pain. It would be nice however if they could have 25 rated bgs once in a blue moon for special events that grant special pvp rewards. Just like its fun raiding faction cities once in awhile, I think it'd be fun to do rated BGs too. But it would be a drain to have to be required to do them every three weeks though.