What I don't really get is the reason why their work is going to be less professional and effective than yours will be; among other things, they're much less likely to pointlessly reinvent wheels.
Really, the critique you're delivering applies only to a couple of the points I'm making, and, subtextually, it really applies primarily to the use of CSS/React frameworks like Bootstrap and Material and Foundation and Grommet. I think an ordinary developer can throw a dart to pick any of those frameworks and end up with better, less-janky, more usable UI than they would get by DIY'ing it first (and, inevitably, adopting a framework anyways).
It's a weird quirk of web development, not shared by any of the other kinds of front end development I've been exposed to in the ~22 years I've been shipping code, that "pro" UI has to be done from scratch. WinAPI and OSX developers get UI toolkits from the platform vendor, and while you might work outside those toolkits for some custom stuff, eschewing it entirely will get you looked at funny.
But use a decent UI toolkit on the web and you're "just gluing third party components together".