Maybe Jace feels over saturated because he's the only blue planeswalker that's gotten serious stage time?
I think it's because of the difference in 'tournament time' (like you said, stage time)- his cards have each been dominant / played in dominant or popular decks, save living guildpact. Blue decks have often been Jace decks for years, and people are just over the same character being in their face for so long. No other walker comes close to his level of viability+archetype popularity as a whole.
The only other walker I have heard people be "over" is Elspeth, Sun's Champion, and that had a lot more to do with shaping the standard meta around herself than the character- people just wanted the card to go away. If Elspeth got enough cards that were played in similar amounts I believe people would begin to hate her as well.
If you count the number of
format-defining cards each walker has had, it kinda looks like this:
Jace- (5/6, 4/6 if strict)
Chandra- (1/6 if the current one stays strong)
Garruk- (2/6 if you're generous)
Ajani- (1/5)
Gideon- (2/4)
Liliana- (1/4)
Nissa- (0/4)
Sarkhan- (0/4)
Sorin- (1/3 eh)
Elspeth (2/3)
By format-defining I mean top-tier decks used them decisively as part of their main strategy, or high counts as value (lookin' at you, baby jace) I'm a bit hazy on how much decks leaned on their
Garruk, Primal Hunters and a couple other walkers, but the vast majority are the "1-2 just because they're goodish" in an archetype, and some players passed them up completely without apparent loss (Sorins, Sarkhans, Ajanis)
So for the random person who just goes to FNMs, they've (typically) had to contend with Jace way more often than other walkers, and even if the card is different, the character is the same. Just gets old seeing the same face in a game that practically specializes in variety and spice. So it's not really that he dominates "the blue walker" scene but the walker scene at all, really.