I think your analysis of the use case matches the mindset of most low-end UPS manufacturers!
Some background:
I have just had FTTP Internet installed to my house. I can use this for, among other purposes, VOIP telephony in place of the existing PSTN copper service. However, in that case with no local power, the phone service would stop, meaning that for example I couldn't call up the power company. So I want to be able to keep the FTTP service up for an extended period. The RasPis I'm not so bothered about, provided they shut down smoothly. The existing FTTP collection of equipment takes 18W, with no PoE load other than the WiFi access point. Obviously, VOIP phones will add to this load, and I plan to add a couple of security cameras as well. But 35W would cover it comfortably.
The classic 'enough power to shut down a PC if the power fails while I'm using it' is covered by a different UPS, in another place. In fact, the Mac Mini is low enough power to keep going for quite a while, although the monitor isn't. Nevertheless, I have this set up to just shut down after a short delay, when the power fails.
The networking equipment is in a central wiring closet, which is quite small and has limited ventilation. It's not really feasible to increase the space or move it elsewhere. There isn't space for a rackmount UPS, unless it's only 8" deep!
Mobile phone coverage here is marginal, at best
Interestingly, BT, our phone company, will stop supplying new PSTN phone lines from 2025 on - they are trialling this now in nearby Salisbury. All (new) telephony service will be VOIP over either fibre or copper DSL, even if no Internet service is provided. From this date, if a PSTN line fails, it will be replaced with VOIP, not repaired.
There are going to be millions of customers who will suddenly discover that if their power fails, so does their phone. At least some will want a UPS...