“First off, there’s the premise that things won’t go well between Tifa and Cloud, and that even without Geostigma or Sephiroth this might be the same. I don’t really intend to go into my views on love or marriage or family. After ACC, I guess Denzel and Marlene could help them work it out. Maybe things would have gone well with Aerith…”
- Nojima, Advent Children interview
The problem with using this quote as proof of either neutrality or Clerith, is that you have to ignore arguably the most relevant piece of information in it, which is Nojima basically telling us he wrote Case of Tifa through his views of love, marriage, and family.
Even if we ignore that, if you want to take the bit at the end about Aerith meaning that Cloud could have had a successful relationship with Aerith, you have to assume that the quote is talking about romantic relationships in the first place, since if it isn't, then why is it that you instantly assume that "things" regarding Cloud and Tifa isn't about a romantic relationship, but that "things" in regards to Aerith immediately does?
and fyi, said "things" that aren't going well is something that is resolved during Advent Children, so no, Cloud and Tifa are not in a dysfunctional, uncompatible relationship, Cloud was depressed, that's it.
It wasn't a fault of Cloud or Tifa themselves or their "compatibility", but mental anguish that made it so Cloud couldn't move on with his life.
EDIT: This is sort of a side note, but you also have to ignore that Barret and Cid talk about Cloud and Tifa in the context of a relationship. I know that the implication on Cid's part about "wearing the pants" is only a localization, the more accurate translation doesn't carry nearly the same implication, but it can't be ignored that talking about Cloud and Tifa obviously got Barret thinking about relationships since the very next thing he says after Cid's implication is;
"How's Shera?"
to which Cid replies;
"Eh, she's the
same."
Another Edit, sorry: Yes, Barret is a third party and doesn't have the final say on Cloud and Tifa's relationship status, but if anyone in Final Fantasy 7 would know, it would be Barret, he has unarguably spent the most time with them out of anyone in AVALANCE. If anyone knows, it's the guy who traveled with them post Final Fantasy 7 and built what is described as Cloud and Tifa's "home" at the exclusion of himself.