^
It's the downplaying tactic. They want to show Aerith is the most special person in Cloud's life by making things exclusive to her and her alone.
Zack wasn't as important because "Cloud didn't mention him much in the OG" and "Cloud only laughs to Aerith" in the course of the game that's why she's much better. This goes to ridiculous lengths such as "Cloud never cried for anyone except for Aerith." The exclusivity then brings out nasty double standards where anything Cloud feels for Aerith is automatically romantic love when his feelings for Tifa is friendship and friendship alone.
When you don't agree, you're in denial, you're not a neutral and you're biased, possibly brainwashed by TLS. Sometimes Cloti is not even friendship, it's just obligation because he was forced to ride on her promise.
True, Zack wasn't emphasized in the OG but even in that game, he really did something for Cloud which is no doubt important. Zack saved Cloud from Hojo's lab even if this means slowing him down. Even in their polygon glory, before dying Zack was checking on Cloud and protecting him. Plot-wise though, it wouldn't be a good idea to show Cloud telling about his friend you can only see in an optional flashback to his party who don't even know him.
And when you point out how special others are, you'll get accused of downplaying Clerith. Because when you try to remind how important Zack and Tifa is, you're diminishing the exclusivity of Cloud's feelings and actions for Aerith because you know, being in love with someone means you should be an ungrateful, insensitive bastard for the friend who died for you.
And lastly, when you try to show Zack's importance, it's a Cloti agenda subliminally bring down Clerith.
So yeah