Ridges? who cares about ridges? Of course it's Klaa. STVI was written so to get everyone on board. Adm Cartwright, who worked so hard during the whale probe crisis, rebranded as the bad guy (I'd call him Cartwright-refit); Sarek hammered into a scene to do essentially nothing just because he is Sarek; Saavik (with her name changed). Clearly Meyer wasn't very inspired and just delivered a custom order by Paramount who was scared VI wouldnt be more profitable than V.
But if anyone really has a problem with ridges, remember Worf himself changed during the TNG run and no one went "hey, who is this other Klingon -- and where's Worf?".
That last forehead change in season five was a big "WTF?" for me. I didn't like it at all. I thought it was too severe. It ended up being my favorite look, though.
If you look at Kurn's appearances, you can see they'd change his forehead to match Worf's.