Not to be the ToS defender here, but I wouldn't call Mithos getting mad at his subordinates for petty things a problem. He is a villain, after all. Villains can make mistakes. And... while ToS wants more sympathy for Mithos than perhaps deserved, it does have some sense that Mithos is a genuine bad guy. I dunno, I can think of lots of worse JRPGs so it's not letting ToS off the hook, but I think ToS was going for more "villain with understandable motivation" while FFX was thinking more "villain with sympathetic backstory who has since gone more crazy." Plenty of games with villains who are objectively crazypants evil whom the heroes "let off the hook" and talk about how nice they are, unfortunately. At least ToS has the sense to let Mithos do some genuinely heroic things in the course of the game rather than just entirely say "oh by the way he's a hero despite everything he does being evil."
The problem with Mithos is that his motivation doesn't make tons of sense, and the narrative doesn't cover this by going "yes he is being irrational here." Mithos basically has two things:
A) Weird Japanese sister obsession, trying to revive his dead sister even if it involves doing bizarre shit like dividing worlds. Sure.
B) Defeat racism by creating a world of lifeless beings = code for magic robots basically. (Shades of FE6 Zephiel or TotA Van.) This is more "Japan sucks" societal commentary I assume.
The problem is that these twin motives undercut each other. If Mithos and his forces are so godlike as to try and solve A - which involves massive influence on world governments, their own private army, etc. - then B seems like a piddly concern. If B is the main concern, then why is Mithos taking his eyes off the prize by worrying about Martel? And then the narrative gets too stuck on this for the last quarter of the game or so, where it basically stops throwing any new twists, or at least good twists. We get it.
I think ToS COULD have made it work better, it just didn't. For example, if they own Mithos's power from A, they could have done an exploration for how despite having ultimate magic power, Mithos can't stomp out racism. Have some sort of failed-Superman thing where Mithos always shows up too late to save some half-elf in peril, and he can execute the perpetrators horribly, but it doesn't stick, and this drives Mithos even crazier, which causes him to think reviving Martel will do the trick instead. Alternatively, just focus on B, make the half-elves more authentically oppressed and Mithos's organization more like terrorists than a shadow government, and power down Mithos some. If you want his sister's soul lying in a crystal in the background as tragic backstory, fine, but mostly skip out on the revival plot this time, and focus on Mithos's goal to stop racism with replacing everyone with lifeless beings or whatever. And make up for less magical power & influence by having him fight dirty instead.
