>Seel > Dewgong
I agree, even though I like both a lot, I admit the Evo line is a touch boring
>Poliwhirl > Poliwrath
I disagree, wrath is distinctly different. Moreover, this may just be for me, but their designs ooze specialties - Whirl seems like a special attacker, Wrath seems like a physical attacker. This is further explored with Politoed looking like a retard (read: some sort of support). The line is very good, you're just mistaking simplicity for lack of forethought.
If you glance at gen 1 (I assume this is your context), almost all evolution lines follow one of three patterns:
>Evolving = "growing up/aging"
>Evolving = "growing stronger"
>Evolving = "more of x" where x is a base identity (for example, dugtrio = "more" Diglett)
The only exception to these three groups is Electrode, which is pretty universally agreed to be a lazy design. Had Voltorb been designed in a later generation, it would have been a single stage gimmickmon serving as it does in Kanto - a trick when you try to pick up an item.
Gen 1 is very cohesive and consistent in these rules, and clearly evolution was a thought-out gameplay aspect.
