the two seem inextricably linked.

Maybe because they are the same thing?

but Wahabi is a derogatory term calling them followers of Wahhab

Well, bless their poor sensitive butthurt asses. Maybe people call them Wahabis for just that reason?

So they have successfully branded Salafis and Wahabis as religious deviants, turning them into boogeymen.

I've never seen that. I'm not sure how familiar you are with Salafism, but there isn't any central Salafi doctrine. Salafi disagree with one another all the time. Munafiq Muslims tend to argue about specifics, but I've never seen them say that Salafis are religious deviants.

Side note: These people have even popped up on /r/exmuslim, and may claim that this argument tries to invalidate our exmuslim experience, claiming we were not true Muslims unless we were salafis.

I'm fairly new to this subreddit, but I've been reading for a while. Can you link me to any of these liberal Muslims in this subreddit? You've got to understand, as an atheist, I'm inclined to be skeptical of any unsubstantiated claims.

and intellectually honest towards Islam

Can you explain that? One of the main arguments I've seen levelled against them is that they are intellectually dishonest by accepting hadiths are being true despite hadiths not having any external validation. What I mean is, only Islamic scholars validate hadiths. I'm not aware of any non-muslim sources that have validated hadiths. I think when non-muslims scrutinise hadiths, they usually turn out to be totally rubbish.

Karen Armstrong loving liberal Muslim who says "there is no compulsion in religion".

I've never seen one of these. Again, can you link me to some sources for this claim?