There are many turners who happily use treadle-powered spring-pole lathes. And I've even seen a belt-driven, waterwheel-powered lathe.
But most of us prefer electrically-operated lathes. They are just more convenient.
Variable speed is another form of convenience. It's not essential, but most of us prefer the convenience of being able to quickly vary the speed of the lathe to the nature of the work being done. Higher speed produces smoother cuts and is important on thin spindles (such as pens), but sanding requires lower speeds to avoid overheating the timber, etc.
The three lathes you mentioned are all good - but the JWL-1221sp is NOT a variable speed lathe - you have to swap pulleys to change speed.
So its up to you - what kind of work do you expect to be doing, and how much convenience to you want (said differently, how much inconvenience are you willing to put up with)?
You seem to be focusing on so-called 'midi-lathes' - machines with a 12" swing and a bed length of about 18". There are brands that you haven't mentioned - Laguna and Turncrafter for example. These are also good. The criticism that with Jet, you are paying for a name could be said of any of them.