That's a great point! It's been awhile, but did we have to do all the Mages Guild, Thieves Guild, and Fighters Guild quests from all of the cities in order to complete them? It seems like we didn't, but I could be mistaken.

You may be thinking of Oblivion. In Morrowind, I was able to circumvent a lot of quests and still rise to the top of the guilds.

Can't remember in the case of the Thieves Guild but in the MG and FG you could miss out some of the quests and questgivers and still reach the top rank. Indeed at one point a questgiver in the MG who had no more quests for you told you you could get quests from her boss in Balmora but might prefer to go to the guild steward in Ald'ruhn instead. There were also a couple of different ways to become head of the MG.

Thanks! I thought so, and kind of recall some of my characters doing both the FG and TG and getting to the "Code Book" quest, then being able to get Guild Leader for both, even though I rarely went through with the "Code Book" quest.

It seems that one just needed to get the "Mages Guild Infiltrator" quest from the head of the Balmora Mages Guild and the second in command in the Ald'ruhn Fighters Guild to finish up those quests

Yeah, Morrowind's guild progression used, in part, a 'Completed Mission' tracker for its ranks, and all 3 guilds (though not the houses, and not the Morag Tong) actually had more jobs available than were required to reach the leadership. Though, I think this was largely due to the fact that none of the factions really had a narrative structure to them, and we're more labour related.