They certainly are discouraging from running small mail servers, because it's harder to hold a small installation accountable. A spammer is usually a tiny installation which would disappear overnight, being run on random botnet nodes.
I don't think they explicitly are trying to quash smaller independent mail servers (personal or commercial), they just see what spam statistics show, and update blocking rules accordingly, maybe fully automatically, using ML. The fact that they also quash small-time independent competition is just a nice (for them) side effect.
They operate since 2007, they can track who is reliable and who is not. It's not like IPs change[1].
[1] yeah, they might be some people trying mail servers on dynamic IP, but I'm not talking about those and Google would have some justification not categorizing them as reliable. I'm talking about using business level ISP offering with a static IP address and matching RevDNS.
I don't think they explicitly are trying to quash smaller independent mail servers (personal or commercial), they just see what spam statistics show, and update blocking rules accordingly, maybe fully automatically, using ML. The fact that they also quash small-time independent competition is just a nice (for them) side effect.