It should in theory be easier to get a 100% IV Pokemon from eggs and raids than from a wild encounter. The reason being that a hatched Pokemon or a raid Pokemon has an IV range of 66.7% to 100%, with its attack/defense/stamina values being 10/10/10 at the lowest and 15/15/15. All in all it gives you a 1 in 216 chance as opposed to one in the wild which ought to be a 1 in 4096 chance.
Until I hatched the 100% Swablu that would evolve into the Altaria you see above, the previous entries in this list except for Moltres were all caught in the wild. Moltres came via a Field Research encounter so the odds are the same as hatching an Egg. So I was very thrilled to hatch this Swablu, especially with it having a Mega Evolution. Whether Mega Evolutions will be added into the game remains to be seen but if they do add them, I’m at least guaranteed to get a perfect Mega Altaria. Altarias are also expensive to evolve, 400 candies a pop so you want to get your candy’s worth before evolving.
Currently Altaria sits around with the other 100% currently not in use. If there’s a Mega Evolution I’ll get around to using it but until then it’ll be here for collecting.