The Jetboil was designed to do a specific job: boil water very quickly and simply. That it does extremely well.
There is no pumping, no priming, no fuel to spill, it is a light, self-contained unit. The insulated 'pan' is part of the stove, and can be used like a mug. Yes, it is like cooking in a kettle but that's exactly what it is: a gas-powered kettle. The idea is to create hot water for drinks, boil-in-the-bag meals, or dehydrated meals like soups and noodles. We're not talking gourmet meals here.
At altitude it works fine - the gas cannister must be warm-ish so is usually carried in a pocket close to the body or kept in a sleeping bag over night. At 4000m, no problems and only a bit of stuttering - not sure how it would do in the higher ranges and I expect performance would start to tail off. This is where something like the XGK or equivalent would be a better bet. It still works well at reasonable altitudes because it is so efficient.
I do not have a downer on liquid fuel stoves - indeed, my MSR XGK is a fantastic expedition stove. However, as stated, the Jetboil is a life-saver and I would suggest that it would provide me with a hot drink and meal long before a primus/XGK/trangia/etc. That is why it is a lifesaver.
My stove may well be around in 90 years...but it's a moot point because I won't be.