I actually agree that they would be a fun civ if the extra TC speed was moved back to castle age and first crusade was gone.I think the Sicilians tech tree is pretty good, there are some obvious omissions like hussar, thumb ring etc. but overall I think it's solid. Arbalest without thumb ring or ring armour are still pretty dangerous, light cav with all upgrades are still a solid raiding unit, you can go fu halb and siege, plenty of flexibility there. And the anti-counter mechanic makes all those options that much tougher to deal with. If first crusade was nerfed a bit I think they'd be a really fun civ overall actually. They do lack an obvious game-ending lategame composition, but lots of strong civs don't have that, e.g. Malians: you just have to play in every age and try and get to lategame in a good position, then use your flexibility to counter your opponent's comp.
TC speed would also be fine if it's just reduced so they don't get it up faster then Spanish on Nomad.