This is just otaku doing what otaku do often, and sometimes best: excessively nitpicking in an irrational way:
They cause some concern: the new anime is no different from the old one.
For starters let’s ignore why he thinks it’s no different from the old one. Let’s talk about rather what exactly is not different. To me Anim@s is a character-driven, series of dramatic set pieces that drives an overall theme forward along. The plot orients around what typically passes for idol industry–development of entertainment talents oriented as musical artists. Will Derem@s be the same? Probably. We’re not going to pilot the Kisaragi here.
But how can it possibly really be all that different? You can’t take the idol out of IM@S–not even out of Puchim@s, which is so far from the Anim@s in terms of outlook and concept. I think Author should just rest assured that there are no Rika or Mika, no Uzuki, Shiburin, or Mio in Anim@s. How can you have same flavors of character stories if the characters are so different?  How can baked turnip taste like leftover turkey?
I’m not sure there is any real reason to assume we’ll get a GBFT, mainly because unlike those two shows Derem@s is just a different concept to begin with. Let’s use the leftover analogy: you might heat up leftover turkey and it could be good, but that would be a half-hearted way to eat after Thanksgiving. Do what my family did: bake a second one. I assure you it will not be at all like leftover. Doubly so when the second turkey is actually a turducken in disguise (well, we actually didn’t). When the work is created with conviction and can stand on its own, I don’t think it’ll be a problem at all. And for the CG anime project to be successful it has to be like that. Take a cue from Bahamut–the two Mobam@s games are wildly successful financially, I don’t see how they can really botch it after getting the production formula down via the various Anim@s projects.
And it seems they are baking a new turkey. They’re putting the limits at 14, which is perfect (if Anim@s is any indication) and will curb concerns about “how do you even do a Cinderella Girls TV anime” issue. The point about taking place in the same world is probably just a way to establish some continuity in character cameo and make collaborations possible (after all 765pro characters are in both Mobam@s games), and not some indication that they are are actual sequels. The fact that they have not said they will be sequels puts it to rest to a degree.
Which goes back to my first assumption: what the heck is the guy thinking that Derem@s is anything like IM@S to begin with? Maybe it’s just a matter of perception. I mean, I suppose it’s not impossible to confuse a pachinko machine with an arcade cabinet.