It's definitely playing with fire. Lapis and B. Iris aren't 100% broken in the strictest sense of "The gameplay is now bullshit" but they are irritatingly desirable. Luckily, they buff units rather than single handedly destroy everything themselves and we're talking about a freemium single player game where people want to catch all the waifus rather than a competitive multiplayer game. So as game warpingly powerful as B. Iris and Lapis may be they're not set up in a manner where you'd actually want to run multiple copies of them to the total exclusion of other units. That means they're fundamentally incapable of completely screwing up the game as badly as a couple of horribly overpowered releases might end up warping the meta of a card game or a MOBA--people might get annoyed that they take up slots virtually by default on the hardest maps but at least they'll never turn some competitive ladder into a boring series of mirror matches. At worst their eventual necessity might drive off a few freebie players but there's ways of addressing that problem like anniversary tickets and power creeping other units.