Overall they're pretty quick on my Galaxy S2. A bigger concern is formatting - some adjust for mobile, others do not and the font is displayed in .5 millimetre type. :(
(perhaps I should apply for a testing job!)
In these last 4-5 months that I have been a frontend dev (angular) and have played around with chrome throttling dev tool and questions by product about load time that I realised how life is difficult for web developers and users in emerging markets.
It's not like one doesn't have to think of load time, performance, and bandwidth in Android but, there, things are quite standard to some extend when comes to achieving a decent level of performance.
One thing I have learned, and still learning, and that is avoid jquery (and esp. it's plugins) as much as you can. I mean they can pile up really fast.
Another thing is that each of these implementations pre-cache most (if not all) of their static resources with a service worker -> and that's why repeat visits on each site is quite fast. Using incognito or clearing the site data and unregistering the service worker and then loading the site as a first-time visit under those throttled conditions will let you easily notice how much faster some of the implementations are then others (for example: Preact and Angular)
Agree with performance on first time loading. Famous ones: Angular, React, Vue felt slow.