1. I'd guess that of all the knowledge a web developer accumulates about HTML and CSS over the years, less than 1% concerns HTML's syntax. Everything else still applies.
2. As a client-side JavaScript developer, what you're actually dealing with is usually not HTML, but the DOM. JSX only resembles HTML rather superficially. It gets translated to a series of DOM method calls. HTML itself has no support for event handling, control structures, composition, etc.
That being said, going with pure JavaScript is of course a trade-off that also has downsides, such as indeed familiarity, and not being able to just paste a block of static HTML into your code. (Though there's a tool to help with that: https://aberdeenjs.org/Tutorial/#html-to-aberdeen)
1. I'd guess that of all the knowledge a web developer accumulates about HTML and CSS over the years, less than 1% concerns HTML's syntax. Everything else still applies.
2. As a client-side JavaScript developer, what you're actually dealing with is usually not HTML, but the DOM. JSX only resembles HTML rather superficially. It gets translated to a series of DOM method calls. HTML itself has no support for event handling, control structures, composition, etc.
That being said, going with pure JavaScript is of course a trade-off that also has downsides, such as indeed familiarity, and not being able to just paste a block of static HTML into your code. (Though there's a tool to help with that: https://aberdeenjs.org/Tutorial/#html-to-aberdeen)