You're definitely right that a popping big is the biggest threat to Kanter currently. They're icing every screen when he plays, even if it pushes the ballhandler middle, in order to both allow him to drop while still taking away the big. That usually leaves the big with a 3 available (although you can veer the guard onto him if necessary, the Cs generally don't).
I've gotten really interested in seeing how the Celtics handle Kanter's defensive limitations, so I went back and watched all his 2nd and 3rd quarter defensive possessions. The short answer was that the Celtics put Kanter on Thompson instead, so the only way the Cavs could get Love involved in PnR was to run a big-big PnR. That failed for predictable reasons (Thompson is a non-threat as a shooter).
At 2:30 in the 3rd quarter, the Cavs finally got Kanter matched up on Love with Nance in. I'm honestly not sure why Brown or Hayward wasn't the one on Love, but he promptly sought out the PnR and drained a 3 as the pop guy. The Celtics then immediately subbed Theis in to counter.
Kanter's actual on-ball defense in the post was quite good. I'm honestly not sure there's a guy out there, reasonably available, who would be better.
A couple other thing that stand out on film in those minutes:
- Kemba (while good at some things defensively) is their worst option in on-ball PnR defense. He often fails to execute the scheme in terms of forcing the ball-handler to reject the screen, and can't really rear-view contest due to length. Not sure exactly what the solution is there except for limiting the damage to floaters as much as possible and having his offense make up for it (it generally does).
- Jaylen is lazy as hell when he's not focused. A lot of Love's good looks came from him needlessly helping on drives that were already contained. If he locks in on defense, that game is probably over in the 3rd quarter.
I get that it's cool to be snarky about Kanter, but he has real strengths, and there are a lot of approaches to mitigating his weaknesses. With the demise of the Warriors, I don't know that there's a team left that he's unplayable against for 15-20 minutes a night.
TLDR; the Celtics have mostly handled the jitterbug guard approach to attacking Kanter. Now to attack Kanter in the PnR against the Celtics current scheme, you need a popping big on your roster who's also good enough in the post to abuse wings. If you don't have that, the Celtics will put Kanter on whoever your non-popper is, and put a wing on the shooting big (Love, Myles Turner, etc). With Jokic and Embiid shooting meh from distance, I'm not sure there's a guy besides AD who can make Kanter unplayable. Maybe Milwaukee if they pop Lopez a ton, but the problem there is that they only really have Middleton as a threat to shoot in PnR, so you can go under against their other guys and match Kanter's minutes away from Middleton's.