AC only supports 5gz, which has significantly worse range and is impacted much more by walls or other solid objects. But if there aren't a problem it's generally better
That's not an accurate statement. "802.11ac" denotes a set of features, and many of them apply to and benefit the 2.4 GHz band. For example 256QAM encoding boosts the max data rate by 20 or 33% on this band for, respectively, 20 and 40 MHz channels.
https://www.cwnp.com/forums/posts?postNum=307358
I always heard that 802.11ac was 5GHz only, and that on dual-band, stations would stick with 802.11n for 2.4GHz
https://www.cisco.com/c/dam/en/us/products/collateral/wirele...
The only problem is that your phone might not be able to talk to your router through your bathroom wall any more. But that capability was always a sign of wi-fi being too noisy—imagine a light that can manage to penetrate a bathroom wall, and tell me you don’t think it’s maybe a bit too powerful for consumer use ;)
Sometimes. 5GHz is great for apartments (where you have lots of noise and a tiny area) and offices (where you have lots of noise and a large budget), but for a villa 2.4GHz usually hits the sweet spot between noise and coverage.
Visible light has a wavelength of a few hundred nanometers; wifi is around 10 centimeters. Material penetrability varies enormously between different wavelengths (and between materials). Harm to humans also various enormously, and in a way very different from penetrability (for example, some wavelengths of UVC are very harmful to human skin but can be almost completely blocked by a thin sheet of clear glass). Equating penetrability with either 'power' or harmfulness is not a useful intuition.
(incidentally, an incandescent light bulb emits on a blackbody spectrum, so some very small proportion of the energy it uses will be emitted at e.g. radio wave frequencies, which will certainly penetrate the bathroom wall)