AngWay It depends on if you're using a VPN or not.
If you are not using a VPN, all the checks and connections are visible to your ISP. Addionally, since you're clearly connecting your phone to the internet, there will be other connections to GOS servers (such as the update checks and downloads) which will give you away to your ISP even if you change the Internet connectivity checks, Attestation key provisioning and Widewine provisioning to their Google counterparts. If you do, not only are you exposed to your ISP, but you also expose yourself to Google more than necessary. So if you're not using a VPN, I recommend keeping the requests proxied for increased privacy.
If you are using a VPN, then everything except the Internet connectivity checks are routed through your VPN (provided that you haven't manually excluded them inside your VPN), thus keeping your ISP from snooping in on them. In such a case, I'd recommend only changing the Internet connectivity checks to the standard Google server as they're left outside the VPN by design and thus your ISP can see them. That way your device won't be making any visible connections to GOS servers outside the VPN tunnel. I'd recommend keeping the other checks and servers as-is through the proxies, as then Google will only see connections coming from the GOS proxy.
TL;DR: If no VPN, keep everything proxied. If yes VPN, then change only Internet connectivity checks to Standard server and keep the rest proxied.