I use OpenWRT on my old TP-Link 1043nd and it works perfectly! There are some new popular routers on the OpenWRT forum that people say work extremely well too. Highly recommended! Try it with Linksys WRT3200ACM and Netgear R7800 and TP-Link C7.
How is it working out for you? I recommended the highest-end model because I don't like lower performance older hardware. But if the older stuff works fine for you then that's fine by me :)
Mikrotik is good for pro installations, but not easy for regular people to use. And their free documentation is the worst I've seen. And I think you only get a month or so of free tech support. :)
You can sort routers by performance here to help choose what you want: https://www.smallnetbuilder.com/tools/charts/router/view
WiFi is blocked by physical stuff and other wifi signals, so it is possible you just live in a busy place. The best way to get around WiFi speeds being too slow is a...
Peplink is famous for dual WAN and user-friendliness, they have Balance 20 https://www.amazon.com/gp/product/B0042210U6/?tag=snbforums-20 and Balance One Core is the newer higher performance one: https://www.amazon.com/dp/B011VDJWSA/?tag=snbforums-20
> random issues
> an AiMesh setup
> I've played with Orbi, Eero, Velop and Lyro
> Have wired connections in basically every important area
You're overthinking this! Meshes have no place here. They're just for when you can't run a wire and don't have a power outlet that works with powerline...