If you can point me to any aspect of the design of FFP that lowers the gap between the biggest and smallest clubs I'd be all ears. I think it does the opposite. At the moment it seems to me to only really target the "financially doped biggest clubs" which I suppose is just City and PSG if we're honest. We're conflating UEFA FFP and PL FFP a bit here, but on competitiveness specifically (and per my previous post), how does PL FFP solve the problem of United's revenue being five times more than the club with the lowest revenue in the PL? United haven't broken any FFP rules, obviously, so FFP seems irrelevant to me in addressing that problem (of course we might disagree on whether that's a problem or not).
City have broken UEFA FFP rules in previous year(s), and we may be banned from the CL. I'm absolutely fine with that, but I'm guessing City's owners won't be, so it might lead to a messy legal challenge. Who knows!
In terms of FFP being refined and improved, I think probably it all depends on what we want FFP to solve. It was initially supposed to be about preventing clubs from bankruptcy but it's evolved to targeting mainly outside investment/financial doping. I'd love to see it evolve further to target competitiveness but I have a feeling that the elite European clubs would never allow that so it's probably a non-starter. It's worth noting that in 2019 City have no issues passing FFP, so it'll be interesting for many reasons to see what direction any redesigned FFP goes in (that might be influenced by any legal challenge obviously though).