I just replaced a residential condo building's fossil gas generator (Kohler 48RCLC), at a cost of ~$24k, because the association didn't perform the required maintenance on it. Yes, fossil generators can be reliable if you do the maintenance and you monitor to ensure they are doing a test run weekly/monthly under load. Lots of people don't.

My Powerwall quietly sits there charged and waiting to be under load, and charges to full when storm mode is activated (or I activate it manually). It has a 10 year warranty, 15 years if part of a virtual power plant (which my storage participates in with the local utility). It requires no maintenance. I also received a 30% federal tax credit for the Powerwall, which the building will not receive for a generator.

Diesel is not the same as a gas generator. There are a lot of things to go wrong with gas engines tbh. Diesel on the other hand will mostly run without too much fuss so long as there is compression and there is fuel.

Diesel lasts longer, but you should also be polishing the diesel fuel to keep it in good condition, which is another point of failure. When fossil gas is available, it is usually elected as the fuel of choice because this is unnecessary (as the generator is hooked up to gas pipelines, and no storage consideration is required). Propane will last forever in a proper container, but poses more storage risk than diesel.

TLDR Diesel generators where you might be without mains for a while and intend to replenish the fuel with deliveries during the outage, fossil gas for use cases where gas delivery pipelines are available (urban, suburban), propane for offgrid use cases (rural, cell towers, etc) where fuel longevity is a concern.

https://en.wikipedia.org/wiki/Fuel_polishing

if you dont have an ICE car, i think id prefer propane over gas? ill likely have the propane tank for a grill anyways

In this context, "gas" is "natural gas" delivered continuously through pipelines directly to your property. Propane is delivered by truck periodically, and stored in tanks on your property. Gasoline and diesel would also be delivered by truck periodically.

I think he is talking about natural gas rather than gasoline/petrol.