We may know the same devices - designed to run Flash Lite acceptably then made to just barely support HTML/JS with heroic engineering efforts later. Nobody believes how slow they are until they try.
I think if someone queries the DOM a lot on these things, especially in response to keypresses, they're in trouble whether or not they're doing it with jquery.
The lowest common denominator I had to deal with were some quite expensive, for the hardware, Arris devices. Roughly 10 times slower than a 2 core skylake and similar. I wish I was joking. As you say, people have no idea what slow is until they have to code for these.
I've played with some fairly decent machines as well. Quite a bit faster and cheaper but you can't just magically replacement millions of devices every time something new comes along
I think if someone queries the DOM a lot on these things, especially in response to keypresses, they're in trouble whether or not they're doing it with jquery.