Dugtrio is literally three Digletts standing next to each other, Poilwrath is Poliwhirl with an angry expression, Electrobe is Voltorb turned on its head. Magneton is three Mangemites stuck together by magnetism. There are some pretty unspectacular evolutions.
But I am miffed that Wishiwashi's school form isn't an evo. Mainly because I really like the idea a giant fish that's created by a bunch of little fishies fusing together.
This is basically my opinion on the matter as well. Stuff like Magneton just being three Magnemite shows that evolution isn't a very strict concept.
Also agree that I would have preferred Wishiwashi as just a straight up collective evolution in the same veins as Mangeton, Dugtrio and so forth. But I don't really mind it being a forme change, it's just a slight preference.