I’m OK with “unified mechanic” RPGs. I don’t think lacking a unified mechanic is a flaw, but I don’t think having one is necessarily a flaw either.
There’s an interesting variant that I’ve seen pop up a few times: Using a linear distribution for combat and a normal distribution for skill checks.
e.g. Someone on the TFT mailing list used a d20 for combat rolls but kept the standard nd6 rolls for everything else.
I think the appeal of this comes from the fact that, the way most people play, combat involves lots of rolls while non-combat checks more often involve a single roll. When you use a linear mechanic for skills, the results seem too random. When you use a normal-distribution for combat, things don’t feel random enough.