It's important to note that this isn't "you have to be big in order to be able to filter spam". That's not true at all; decentralized anti-spam lists have been a thing for decades and the big sites don't have any significant advantage in filtering spam.
It's allegedly that big sites will mark small sites as spam even when they're not, which makes it hard to run a small mail server. And there is some of that -- they also have a perverse incentive to do it on purpose because it kills their smaller competitors.
But it's also somewhat overstated. If you have a reverse DNS entry pointing back at your mail server and have properly configured DKIM, it's not inherently the case that you're always going to be marked as spam. And it's not inherently the case that you won't just because you use one of the big services -- they have the same incentive to do that to each other, after all.
You saying the average admin is gonna have no issue setting up their MX records but “won’t even know” what a reverse DNS entry is?