Thankfully, persona levels really hardly mattered much, especially in the games you can raise a persona's stats. Surt, the ultimate Magician, was my main damage dealer the first time I played FES for example, even at like lv60.
I guess that's true, it's not too bad in P3 to keep stats up endgame because you can just raise your stats playing games/using cards and it's all good (especially since endgame you don't have much else to do at night), so that way they can keep up. The only real problem I guess is that by the level you get them I think you have access to null elements, but not really any repels, absorbs, or in general other high level passives you may want to put on them. I'm pretty sure I had Odin with close to max magic for thunder reign spam and Siegfried with max strength for vorpal blade spam, so their damage was high, though their other stats weren't so great. But because I fused Odin at mid 50s in September-October and didn't want to fuse and grind a new one for thunder reign, it only had resist/null wind since that was the only way I had to cover his weakness at the time, and I didn't want to fuse something else after all the games/cards spent on him (and if it was like P4 I wouldn't be able to transfer it). But Norn, who's ~10 levels higher learns absorb elec and Skadi ~20 levels higher learns absorb fire (It could be coincidence though, in terms of the personas learning better passives and being higher level. Odin does learn spell master after all, so maybe it's a trade off?). I'm not sure if it's a problem in Golden, but in vanilla the stats are harder to keep up for the lower level personas without the games/stat cards imo, especially for those that learn the severe magic spells since they're not necessarily the final personas of their respective arcanas (Surt wasn't, even though I think he's better than Mada and should have been made ultimate magician. Thor wasn't, but to be honest I didn't like him due to his somewhat higher emphasis on strength that he can't take advantage of with thunder reign). I can imagine it would be somewhat worse if the levels were scaled poorly in P4 when they are compared to Odin and Loki since leveling up takes a while after a few level ups, but I don't recall any ways to raise Persona stats. Even then I don't recall using Loki much, though it could just be his stat spread.
Though of course, earlier access to severe elements skills is always a good thing for the boss around that part of the game. In P3 at least you can transfer the skills to higher level personas if you wish so you could always have a persona with the severe element spell at your level with relatively high offense and up to date passives. After all, in P4, (where you can't transfer the skills, Ragnarok and Thunder Reign are stuck on lower level personas compared to Niflheim and Panta Rhei, and also Thunder Reign is stuck on a persona that does not excel in magic while at least Surt does) by endgame most forms of damage are inferior to Hassou Tobi anyways, and in P3FES they were all inferior to Victory Cry/Spell Master Armageddon.
But then it doesn't even matter much since the game doesn't require you to have the absolute best skills with max stats anyways. So I'm not sure where I was going with this.
