I've never heard of a gun with dovetail lumps going off face due to the dovetail, just the usual interface between hook and pin and the bites wearing down, same as a chopper lump gun would go off face. I'm not sure it's even theoretically possible as it would imply the lumps have shifted in a way that means they would have to break loose for the entire length of the dove tail at which point the whole thing falls to pieces.

I have heard of dove tail lumps coming loose on very cheap guns. Never on a good one. I've seen plenty of cheap guns off face due to abuse and/or soft metal in the lumps, pin and bites.

My personal prejudice is against the monoblock as I think the seam between the monoblock and the barrels is unsightly.