I'm not concerned about them being able to stop transactions (at this point anyway),
I just don't want them to know who is transacting with who. The fewer P2P transactions there are, the smaller the data set they have to deanonymize.
it goes back to the fungibility conversation. The more KYCed and known-by chainanalysis transactions exist, the lower the fungibility is on Bitcoin.
but like you say, we don't have enough clear data to really know what the proportion of self-sovereign usage/custodial or KYC usage is.
but unless people start making positive steps to increase their privacy, that proportion will turn toward zero.