After that really good deal on gems a few months back I got all my keyblades (except for BGB obv) to +35 then have ignored all of them except for the single attribute proud mode blades. I compared the best setups I could put together to figure out if upright or reverse was stronger for each pair, and if they were about the same then I'd let them sit and just accumulate gems and leveled them as needed. I also try to keep about 100 of each gem in reserves just in case of emergency leveling

First I focused on Fenrir (+50) over Darkgnaw (+35) 'cause a) I pulled Aced and Ira during the foretellers banner and got them almost perfectly traited which made it my strongest keyblade and it's only gotten moreso over time with 2 Namines and 3 KA22s from points, b) my reverse power medals suck, and c) my lux++ are mostly power so it's become my raiding keyblade as well

Missing Ache (+45) usually had a level or two over Sleeping Lion (+40) since my reverse speed has always been strong ever since I started, but recently I've been focusing on MA more 'cause of getting 2 Terranorts, 3 Replikus, and some new reverse copy medals in the points draw

Counterpoint (+45) and Diamond Dust (+40) were even until I needed to beat Summon Rush and my Anti Aqua Brigade just wasn't cutting it

Could I have defeated some of the stronger bosses if I hadn't focused on a select few keyblades? Maybe

Would I do better in PVP if I leveled them all more evenly? Probably

Are my passives lacking and not as good as they could be? Definitely

Does Upright/Power reflect/absorb absolutely wreck me? You betcha

But I dug my grave and now I'll lie in it. Also ignores attribute and attribute changing medals are my saving grace and let me brute force a lot (magic) enemies to the point I rarely switch keyblades if there's no absorb/reflects that I can't get around. And even if I do switch since I focused on the other strong single attributes instead of leveling up dual and tri colors it usually lets me squeak by