My hairy clients include few cushingoid yaks, my own Connemara pony cross and a large, draft cross. I do not have an issue with it getting through the coat.
I have a reputation for my client horses to be super clean and being in NC and we typically have the resources to get that done. (Rarely do we have any more than a few days below freezing so we can bathe with warm water, wrap in coolers and graze in the sun or dry in a stall very easily). If baths aren’t an option, perhaps they wouldn’t work so well?
Most of the time I am clipping these guys year-round (cushings horses) or early fall due to our show schedule. But I have also successfully clipped a few in February when we had unexpected warm stretches where some of our old guys were just melting in their heavy coats. YMMV.