That seems very optimistic when compared to some of the bigger engineering projects we have going as humanity. Aircraft carriers and nuclear submarines as a whole system (including the multiple computer networks and their software) are much more complex than browsers, to say nothing of one-offs like the ISS (lots of cutting edge hardware but also full of software) and the systems controlling modern factories. Browsers don't even come close.

I think it's kind of hard to quantify complexity in a way that compares nicely across domains. For example, a lot of the complexity in a browser comes from needing to service ~billions of users across thousands of devices using loosely implemented standards. This is quite a different problem to building an aircraft carrier, where you're going to run in to hard engineering and physics problems but you only have to target ~10k well trained users.

Web frameworks are nowhere near as complicated as browsers