Do you honestly think the current writers on the show are the same guys from 12 years ago?
Most of them actually are, sans a few.
Bulbapedia lists all the writers/directors of the anime, in case you want to research it.
Having said that, I'm not too sad over Gliscor's release. Being the unfortunate 6th member, I often forgot he was even in the team like Snorunt back in AG, and the few times he popped up he lost most of his battles. Anyway, its not like Ash forced him to stay either, Gliscor chose to remain to get better.
The difference is Snorunt/Glalie was only around for like 15 episodes, Gliscor was on Ash's team for almost 100 episodes.