Depends on where you are. If you're in the US, sure, there is at least the theoretical possibility of legal protection against misuse. If you're elsewhere, they're not very different, and Yandex at least doesn't already have a million other data points about you to connect with this and build a bigger picture about your life.

The issue here isn't privacy but independence from a specific provider. If privacy is an issue as well then you should be using encryption as emails are not private.

It doesn't have to be fully trusting or not at all, there's different levels. I think using a provider you trust more (In my case Fastmail vs. Google) is a fair tradeoff. Fastmail has a pretty straight forward business model that makes sense to me so I feel like they don't have a reason to scan my emails for ad purposes or else.

Of course if you are worried about some nation state looking into your emails you should encrypt them and use whatever provider.

If you aren't in the US, then Yandex is probably safer.

Russian companies cannot refuse data requests from the Russian government. American companies can.