It's at least a little bit of a gacha game specifically when it comes to the egg mechanic.

The number of eggs you can have is limited, and the best way to hatch more eggs is by paying money. You can't guarantee that you'll actually get the Pokemon you want out of the eggs, it's luck-based.

This is admittedly only one minor slice of Pokemon Go gameplay, but it's certainly a mechanic where you pay money for an extra chance to gamble for something from the loot pool. I don't think it's fair to say it's not a gacha game "by any stretch", given this mechanic.

Actually I'd go even further and say that it's not just the eggs. Buying incense grants you encounters, and there is a chance those encounters will involve a rare Pokemon you actually want -- again, this is very close to getting a chance at a Genshin Impact character, this is basically paying for a lottery ticket for a potential rare character.

Sometimes you need to obtain a specific Pokemon to complete a quest, and the only way to speed it up is to use things like incense and eggs, so progression is actually blocked by a luck-based mechanic where you can pay to improve your odds.

Don't get me wrong, I agree with the fundamental spirit of your comment, which is that Pokemon Go is not a pure gacha game, as opposed to something like Pokemon Masters. But I think it's important to not ignore the fact that using money to gamble for a chance at rare Pokemon is fundamentally a feature of Pokemon Go.