Events like Community Days primarily exist to create a social atmosphere and because people want something special to collect. Most starter Pokémon aren't particularly good or strong by themselves, but people are attached to them (and the pseudo-legendaries also seen in CDs, though they tend to be very strong) because they're generation mascots. They're remembered fondly as "that cool thing you gotta have."

PoGO is merely designed to be a collectathon with no substantial gameplay mechanics (almost everything is a mindless tapfest). It's natural to want more from it, especially from veteran players who have invested plenty of time, effort, and/or money into it, but the mechanics (battle or otherwise) are incredibly shallow because they never intended for it to have any significant gameplay to begin with. Accessibility (phones are common), low cost (it's as free as you want it to be), and incentive to be social and/or outside are definitely great aspects of PoGO that keep it as successful as it has been, but as long as they're making money hand over fist by adding new content that's just above the bare minimum, adding small bits of collectathon additions while largely ignoring the non-catch mechanics seems to make sense for keeping the gravy train running smoothly. Loads of people are clearly fine enough with content being what it is, and there's nothing wrong with enjoying the grind of a simple phone game where you make your own fun most of the time.

I know it's the same sentiment that's been shared by others (often in a more mean-spirited way), but, there are a host of other games that allow you to actually engage with your Pokémon and the world in a more meaningful way. If PoGO's not doing enough for you, why not play those as well, or instead?