'Gaming routers' is pretty much just a branding thing.

Ultimately best performance will be a decent 'prosumer' router that can traffic shape (e.g. implement CAKE) in order to keep ping times down even when the link is under load and then good switching and wifi for the internal side of things (modern wifi standards, gigabit(+) ports).

opnsense would be fine for the former (as would OpenWRT on a pi4, say), and then you need to plug in some decent access points like tp-link eapxxx range or unifi, ruijie etc. That combo should outperform one of those gaming routers that look like an upside down robot spider thing. Well, it won't be worse and it'll be more fliexible at the very least.

Also remember that your dad's gaming device should be hardwired for best performance no matter what you end up going with.

Really this is more a /r/homenetworking thing, they'll have plenty of advice for you to, inc. hardware recs.