I find it really tedious to do a total of 20 side quest in 5 holds in order to finish the thieves guild questline and be guildmaster. I dont mind the 'special' quest for each hold, but the 5 quest for each hold is too annoying. Perhaps a mod that eliminate this or reduce the number of side quest?

There's a mod that allows you to choose where the side quests are. But I don't know of any mods that 'reduce' the content in the game.

I only do those needed to get Linwe's armor, which is imho the best looking thief armor in the game: sleeveless, unique hood, unique color. On top of that it possesses more useful enchantments that those provided by the thief armor.

Aside from the satisfaction of having finished a guild, you gain very little by becoming guild master

Sadly thats kinda my feelign with every guild in Skyrim

In oblivion you felt a sense of acomplishment for finish a guild Dark brotherhood had special items for killing in a certain way

Thieves guild you gained an item that made you basically unable to gain a bounty with it not on as long as you have it on to commit crime.

Mages guild was alot more than jsut a oh hey Ill come sneeze over here for about 30 minutes

And then the Fighters guild had alot more to it.

+ there was an arena that could be considered a guild.

Only guild that has somethign decent is Maybe companions for the werewolf but even that I would only get for the Disease immunity.

I felt very let down by the whole thing