According to this 2021 re-review it’s still fine: Asus RT-AC68U Review (in 2021): Still pretty epic – MBReviews . Since $100 is less than the normal cost, I’d consider just paying T-Mobile
It supports 1.9Gbps on paper. If you’re not saturating 1Gbps, it might be an issue with your client, or with contention in your apartment building. Wifi 7 is supposed to handle interference much better but that hasn’t really improved between 2013 and today