Why would you not be able to build a "web analytics tool" with what parent comment mentioned? At the end of the day it is just data and if you are just starting out pretty much anything will scale and if you already have millions of customers you also have capital and people to think about how to make some homegrown solution to specifically cater to that.

The market for these new breed of frameworks is not huge companies with crazy scaling needs but freelancers and your very early stage startups who haven't even found a product market fit since they are starting new they don't have anything to loose with newer stuff and chances are that newer stuff also helps them do more quickly like I haven't used convex but on it's marketing page it does mention a lot and same for other frameworks like pocketbase or SvelteKit combined with a db etc. Like always there is no silver bullet and every stack can seem "random"