Tucker was solid but nothing special. Remember Buster Douglas was beating him fairly easily until the stoppage. Witherpoon hung tough with Larry Holmes (who was still pretty much prime), and many think Tim won that fight. Witherpoon is a different level of fighter.
I've never watched Douglas-Tucker all the way through tbh but it was dead even on the cards and a 228lb Douglas was certainly no slouch. And, of course, Tucker got the stoppage anyway. Remember Witherspoon was life and death with Thomas and Tubbs, too - i think it's putting too much weight on one night to say he's a level above Tucker or an in shape Douglas, personally. To me all those guys are quite evenly matched on their day. In 87, 88 I'd lean towards Tucker by close decision.
I think on their best nights Spoon takes it, but in real world I'd give the edge to Tucker because of Timmy's inconsistence
