This runs contrary imo to a lot of people's experience with for example Google Mesh, which is a product that I dare say works quite well for most people & most devices.
Agreed that signals like RSSI are device dependent. And open source software like DAWN is not the best at adjusting to this automatically. But in principle, most devices will give your AP a sounding map on request, and most clients will obey instruction to move to a different AP. Even really bad devices have generally worked ok for me at this.
The counter advice if use the minimum number of APs leaves pretty large zones of bad reception, and still already accepts the problem of roaming for many people. It's my hope that open source et al get better, get more competitive with what is clearly possible, especially given that we seem so well positioned to have control that could make good decisions here. To give up, when we have so much rich data & options, does not tempt me.