It does look like Kemba is back to his old self, which is great either way. There's a reasonable argument to be made that Kemba is a top 30/40 player and a top 10 point guard in the NBA in that case.
However there's a difference between regular season basketball and playoff basketball. The defense tightens, more half court play and weaknesses get exploited. We saw it with Isaiah Thomas who was the spearhead of the Celtics during 15-17, but couldn't get it done in the playoffs (aside a game here and there). The guy who carried the team was Al Horford.
When you have a player that has a specific weakness. Being undersized, inability to shoot, inability to switch on defense or defend pick-and-roll, then teams will haunt that like a shark who smells blood. It's why the Sixers let go of JJ Redick, despite him being a formidable weapon in hand-offs with Embiid.
The lack of defensive switchability of Walker is a problem. The question is whether his offense makes up for his defensive vulnerability. With his good but not very efficient scoring and his average playmaking skills for a guard I don't believe that is the case.
There are still a lot of games to play, but I expect that at the end of the year the following teams will make the playoffs (based on current records, point differential, injuries, betting odds and strength of schedule).
East: Brooklyn, Milwaukee, Philadelphia, Miami, Boston, Toronto, Indiana, Atlanta
West: Utah, Phoenix, Denver, LA Clippers, LA Lakers, Portland, Dallas, Golden State
The respective point guards can be sorted into 3 groups. Stars, small group of players who are better than Walker without question and yes that includes a guy we dislike in Irving. Above average point guards I prefer over Walker mainly due to defensive versatility. And the third group consists of point guards who I believe to be inferior to Walker.
Stars
Irving (Brooklyn)
Young (Atlanta)
Lillard (Portland)
Stephen Curry (Golden State)
Prefer (mainly) because of defensive versatility
Holiday (Milwaukee)
Lowry (Toronto)
Brogdon (Indiana)
Murray (Denver)
Conley (Utah)
Paul (Phoenix)
Inferior guards
Seth Curry (Philadelphia)
Dragic (Miami)
Beverley (LA Clippers)
Schröder (LA Lakers)
Richardson (Dallas)
So I'd take 10 of 15 starting point guards over Kemba and that makes him a below average playoff starter in my book and not worthy of $35M a year for the Celtics.