Just to provide some perspective for 4/32. No, I did not omit the firewall in that example -and never will- but those are the limits (and keep in mind, we are preparing for kernel v6.6, so add another ~600-800 KB to the tally). Not a small percentage of those who are asking for 4/32 support do not restrict their envisioned usage scenario to AP-only functionality, quite a lot do expect to use them as router as well - that's the hard line I draw into the sand for myself, I will not sacrifice firewall or IPv6 support, anything else may be let go for the sake of an experiment.
Another thing to consider, 'old' APs do litter the scarce frequency band more than 'modern' ones - yes, modern ones will use larger channel width, but they're finished quicker and then allow others including your neighbours to use the airtime. (<=) 802.11b is the worst offender here, given the different encoding and 22 MHz channel bandwidth, but the same also applies in any situation where you mix very disparate device generations with each other (I'm not complaining about the odd client here or there, but about the infrastructure devices, the APs) - and the effects of a 'rogue' AP go three times beyond the distance you scan 'see' (scan for) them. So for your own benefit, keeping your old devices running might do more harm to yourself, than you might expect.
Power consumption is another topic, yes modern routers are likely to have a higher power draw than your old ath79 doorstop (802.11ac/ax/be radios are power hungry, even more so with 2, 3, 4 of them per device - before even thinking about proprietary 'mesh systems' with 2-5 satellites operating), but devices of the wrt-54g(l) era vintage had rather ineffective transformer based PSUs, while more modern switching power supplies do waste less electricity.