What you have will have the same broadcast strength as what you are buying, that’s how legally defined power limits work, and what you describe sounds pretty minimal in terms of client count and coverage area - have you checked the channel and made sure it’s set to the quietest non overlapping channel for 2.4 and 5Ghz to something not in use?
I would strongly suggest more research, start by placing less weight on sources that don’t specifically state they received no consideration in terms of free/subsidised hardware. ASUS is a marketing company, they haven’t made good products in decades, especially networking products. The manufacturing/QC sucks, the CS sucks, the RMA sucks, the history of abandoning products after telling people they will fix issues sucks, the unwillingness to patch known security issues for years sucks, the faking of FCC test data sucks. Yes, other OEM’s have issues, but I literally cannot think of one who gets it that wrong, that often for that many years. Admittedly running 3rd party firmware on the hardware does remove many of the issues in question, but that’s about the only time I would consider ASUS hardware, and even then I would be pretty selective.
You say you want a better router, but only complain about wifi, so - other than wifi - what exactly is your current router not doing that you want? If it is only wifi then run a cable to a central location (usually upstairs landing) and mount an AP on the ceiling, it’s quick, cheap, efficient and makes future upgrades easy. Mesh is cheap, good mesh isn’t. Good mesh should come with a wired backhaul, OK mesh should come with dedicated radio backhaul, cheap mesh will be sharing backhaul with clients and that’s not fun.
