The answer matters little to the novice. You say that you "love thinking about building startups and the web projects." Have you ever built either?
Become an engineer. Learn to design solutions to problems and implement them (on the web or otherwise). As you study, pay close attention to the patterns that begin to emerge. Think about abstractions of those patterns and potential methods of composing them. Technologies, platforms, frameworks, etc. tend to come and go on inconveniently short timelines these days, but the concepts from which they sprung usually endure to see multiple implementations.
If you enjoy development, start with web and learn other technology. I've been writing code for a very long time and have been a founder more than once. The key I have learned myself and from others is if you keep learning all the time, you can always find a home someplace.
Also remember, web development in enterprises is slower to change than in startups, so even say startups see web dev decline in 10-15 years in favor of some new tech or mobile only etc. Enterprises will still have positions and needs beyond that as they trail the startups considerably in changes, for valid reasons.
I agree not to get caught up in the idea one developer specialty is better than another, they are just different and have different complexities.
In the end, the OP learning web dev is a great lower barrier way to enter the market and learn and find what they really want to do/build.
Also, translating the requirements into good delivery is pretty crucial now, a web programmer is expected to take on a lot more ownership of the product/project they work on. But like @davismwfl said, it is here for long to stay. Good luck!
Are you committed enough and talented enough to survive that shake-out? Or will you wind up like the fellow in the apocryphal "Will code HTML for food" pic that's been floating around the Internet since the dot-com bust? Only you can decide that.
Really? 19 years ago was the start of the dot com implosion and the wailing and gnashing of teeth from suddenly unemployed web developers trying to find new jobs was well nigh deafening. The drought of jobs lasted for several years.
I'm very bullish about the future for web developers until we see the web contract as a platform. And I think we have a long way to go until that happens.
* The web isn't going away.
* Even if mobile/AR/voice assistant apps dominate the world, they'll surely use an extensive web back-end.
* The web programming skills you have will transfer to mobile and beyond.
It seems to me that everything things that's not embedded or OS development is Web and by that definition I'd imagine 75%+ of developers are "web developers"
What I would advise against is to read too much into the feedback you're getting, because none of the posters know you or what you're interested in. "Web programming" is incredibly broad. At the barest minimum, it could mean "websites", i.e. HTML/CSS, or database-driven website platforms like Wordpress, so HTML/CSS/PHP and a bit of MySQL. But these days it could also mean Squarespace, Wix, Shopify and other platforms with e-commerce capabilities. If you're at a medium to large company, those roles might split further into front-end and back-end development work.
If you are thinking about startups, I'd advise you to read into the history of successful startups, and get an understanding of the basic business stuff, like what the product was, what the market was, who was part of the original team, things like that. A great reference for this is the 2007 book Founders At Work, which has detailed interviews with people at big dotcom era companies like PayPal: https://www.goodreads.com/book/show/98233.Founders_at_Work
Maybe that can help clarify your thinking a little bit and help you figure out which slice of the pie you want to be in.
More importantly, at 17, you don't have to decide anything right now and all the time to explore. The first step to building a web startup might be to actually make a website about something you're interested in. It doesn't have to be something that makes money, but it should involve a learning experience of some kind.
For example, let's say you create a Wordpress website, put up a few posts, and realize you hate the way the default theme structures the layout. The next step might be for you to mock up your ideal layout in a free tool like Figma (or just on a piece of paper), and start looking up HTML/CSS tutorials online to move beyond the mockup to working code. Down the line, you might want to start hosting your website on your own server, so you could buy a hosting package, learn how to connect to a server, and upload your website's files to that server using FTP or Git. Either way, you'll learn a little bit about how these different pieces work.
Reading and Thinking is maybe 20% of the learning equation. 80% of your actual learning will be by trial and error when you're actually trying do make it happen.
@DHH at startup school, still a great talk and still relevant.
Check out this podcast:
Lots of good information about building your own web projects and startups.