Yeah Gmail is actively filtering smaller providers. But from what i heard/read it appears after personally contacting them several times they will end up allowlisting you (like Microsoft).
Arguably, if you're operating a business and have a client using Gmail, you could have you and your client contact Google support to ask allowlisting, then sue Google for anti-competitive (monopolist) behavior if they don't comply. I don't know of a case like this, but it should be an easy win and would set an interesting precedent.
I'm personally not into legal stuff, but if some startup people around here with a few lawyers would try this approach... :)
"We have received many reports from GMAil users that our messages were not delivered or delayed. Please provide an alternate address."
Somebody who knows somebody will see that and poke their contact for you.
Personally i don't care that Google won't let me talk to people. I treat google's email server like i treat a bourgeois café in a fancy district: there may be friendly people to have a chat with in there, but they definitely don't want me around and i have better places to be and better people to meet. Only a revolution can change this balance, and in the meantime i won't loose my energy trying to get into their club, but rather develop our decentralized clubs.
Using SES with the exact same emails, Gmail will block significantly less. The large providers are whitelisted and unless you're as large, you're not going to get that privilege.
Granted, for $200m you should be large enough to bribe a few Google people to get into the club, but for anything where it reasonably might be profitable to run it yourself and employ a sysadmin, you won't be able to afford that.