I imagine the anonymity set would be much smaller for these combined transports... fewer people using them.
In my understanding, the anonymity set doesn't apply to use of PTs since this is only at the entry side. The exit side does not know[1] what PT the originator is using, so is unable to use that information to de-anonymise.
[1] at least, in theory should not know, perhaps someone can check there are no side-channels? would be pretty scary if exit could work out that originator is using PTs.