The J's + Kemba doesn't seem t be a fit. I will say "Kemba 6th man" would work. He would hurt other benches.
I'm big on Pritchard, but, I assume Stevens wouldn't start him until next year or whenever.
Smart
Brown
Fournier
Tatum
Robert
It's not that we haven't seen this group together when Walker is out except for Fournier
Walker
Pritchard
Langford
Kornet
Semi
This year's team just isn't happening.
For a brief period this bench group "got it going"
Tatum+ Teague- Pritchard - Robert - Semi
This year's team needs a "good bench" that can carry them once in awhile, but won't lose ground either.
I think Walker off the bench would be a plus for the team.
When Smart is "perfect" which isn't that often, he "leads/runs the offense and does a good job.
The modern NBA "run the ball through whomever" is fine, but why not run it through a distributing point guard who "requires the ball"
just to see what happens.
What we're doing now isn't working and thus...chuck it for another approach.
We keep talking about this like it was Kemba's first year but he played alongside Tatum and Brown for most of last year, including the playoffs when he was our best player the last 2 games against Philly. Here's his stats vs Philly:

In fact, Toronto were so worried about him last playoffs that they deployed a box and one to keep the ball out of his hands and rub him out of the game. A box and one is a zone-and-man to man hybrid deployed against teams with one great offensive player, to negate him and force the others to beat you. 4 guys in zone and one following Kemba everywhere. Kemba was the guy they were worried about, not JT. And it almost worked, they pushed us to 7 games. And Miami used it interchangeably to beat us since Toronto had a lot of success with it.
I don't necessarily agree with the "Kemba is a bad fit" narrative, it's too simplistic. He was a fine fit last year. He's just not shooting well right now and I think it's mental. He's become hesitant and indecisive. As the Jays have been ascending and required more usage, he has become inhibited and sometimes he defers to them too much. If you look at his splits between this year and last year:

You can see drops in both his FG% and 3FG% this year. His numbers were skewed by his first few games when he couldn't hit the side of a barn. But even taking that into account he's shot around 40% overall and 35% from 3 which is on the low end for a score first point guard.

By comparison Kyrie shot 51/40, Steph 48/40 and Harden 46/36. Even Tatum shot 45/38 and Brown 48/38. Kemba just needs to figure out why his efficiency has dropped. I don't know if it's the quality of shots he's getting - you could use the Hayward argument, but Hayward wasn't on the court for the last 3 games of the Philly series. Then again neither was Ben Simmons, we have to consider that too.
Also how many players have ended up being "bad fits" next to the Jays? Kyrie, Gordon, now Kemba? Everyone who plays next to the Jays becomes a wilting flower? At this point we will run out of players to pair with them if everyone is a bad fit.