You do realize I hope that this is a most dangerous reasoning?
And your analogy is wrong. This isn't a "lesser anonymity", it is still total. There is just disambiguation between multiple AMs.
Think of it like double blind drug trials. No one suggests that the active and placebo pills should not be labelled A & B. And there is no reduction in the efficacy of the trials by doing so. No one is the wiser by their having been labelled rather than distributed unlabelled.
And there would be no loss of anonymity by allowing us to distinguish between the posts of two (or more) AMs within a thread.
If you want to avoid the crosstalk, use your PM-identity.
The beneficiaries of the measure would be all those who do use their handles, that engage in conversations with AMs.
That is, this isn't aimed at benefiting the AMs -- though they might be glad of not having to add annotations like "I'm the original poster", to their posts -- it is aimed at those conversing with them.
Honestly, why would someone use the AM option at all?
There are good reasons for the AM option. And none of them would be compromised by this.
The only reduction, is that of the current possibility for one person to pretend to be multiple people -- either arguing with themselves; or coming out in support of themselves -- and the only uses for that possibility are trolling and sock-puppetry which are universally recognised as bad for PM.
Reducing abuse whilst protecting identity should be seen as a good thing.