Replayability is important in games these days. But, Skyrim is huge and can take hundreds of hours to see & do everything. Are you going through the same missions with all your characters? If so then I am currious to hear if something different happens.
in my experience it's completely different
on my first char I did a bit of the MQ before going off to complete the mage guild
on my second I did the companions and am now focusing on the MQ
and on my latest character I just ran straight for riften to do the thieves guild, haven't even touched the MQ
only overlapping factor between the 3 is the MQ (which is why I haven't touched it yet with my latest char)
also did a lot of stuff along the way and it was mostly different since I went in completely different directions
do recall seeing some of the same dungeons and stuff but it's still different because with some characters I had a quest there and with others I just looted the dungeon
I feel not being a jack of all trades pays off because it forces you to play differently as opposed to just relying on your strongest tactic
my warrior is like 10 levels lower than my mage but he kicks ass, probably wouldn't even use magic if he had any