I'm sorry, but this article is silly. Why would they start dumping in summons from other games? Pandemonium is unnecessary because Typhon already exists. Yojimbo and Anima are from a game with a wildly different art direction and wouldn't fit at all. Zalera is a zodiac-oriented summon from Ivalice and would also be out of place. Ragnarok is Cloud's second strongest weapon in the original FF7, so it wouldn't make any sense for Cloud to summon his own sword. Sylph, outside of healing, would be redundant.

Of the ones you mentioned that aren't in the original game (and of course they'll be there), the only one that might make sense is Diabolos- but he would be useless in boss fights, which are unaffected by Gravity. Beyond that, this article feels like very little thought actually went into it. Where's Typhon? Why no return of Leviathan? It feels like you went through the summon page on the FF Wiki and picked the ones you thought looked cool without any consideration as to how well they actually fit into the FF7 world.