MikroTik hardware is nice but that company has a serious case of nih syndrome. This manifests as a lot of cryptic, undocumented commands plus the occasional showstopper exploit (eg https://nvd.nist.gov/vuln/detail/CVE-2020-13118). As an added benefit, they have a cult of online followers who are all too happy to deride anyone who points these (and other) flaws out as a clueless nontechnical moron. Fwiw I'm transmitting this through one of their routers.
That CVE is for third party software. But this brings up a good point. It has a good API surface you can plug into in many ways.
There have been some CVEs, but all the exploits I'm aware of already had patches and were only exploitable for un-updated models.
I honestly don't know what you mean by not invented here. They did create a wireless protocol for point-to-point products with some advantages for those who opt into it, but that's the only thing I can think of.
Sometimes their documentation is lacking, but generally their docs are very good.
Still using the hAP ac that I ordered 5 years ago and it works great.
After some time I needed more ports, so I added Mikrotik switch in the mix that gets powered by hAP ac PoE out port.
Great hardware and great software at low prices.
The majority of client devices are 2x2 or even 1x1, so for most setups it won't make much of a difference, if any at all.
If you need a more advanced AP, you probably shouldn't be looking at all-in-one devices. Buy separate components, add as many APs as you need for proper coverage, rather than relying on a single device to cover everything.