But are the designs lean or bloated.

If Figma helps building lean designs it's good otherwise not.

Designers tend to put too much useless parts into sites, like unnecessary transparencies and animations.

that's like asking if a pen or keyboard lead to bloat. depends on who's using them.

More like if AI leads to spam or if guns kill people.

The latter one is harder if you only have a knife instead of an assault rifle.

No it’s more like, does vscode lead to better code than jetbrains? Figma doesn’t really provide meaningful constraints on a design that would let you identify it as Figma sourced, much as you won’t be able to tell whether a site was written in a particular IDE.

You seem to have a fundamental misunderstanding of what Figma is. Your question would be better answered if you took some time to look at figma, rather than looking at the designs people create with figma.

So tell me why the UX in the web gets worse if all these tools and framework make the DX better?

On mobile I have a limited data plan and the speed isn't always the best and on many pages I have to wait because beside the ads I have to download 3, 5, 10 or even more MB of data just to get pages where button, links and headline are undistinguishable because of recent design decisions.

Seems to me these tools are worthless in the end, if you are a user. After bootstrap it went pretty much downhill.

It's good with SVGs, themes, grouping elements into reusable components from your design system, and doing an art board per screen together so you can get an idea of your workflow through the app.

Not great at animations, not great at fully exploding all of the app state. Overall pretty good middle ground for designers and devs to interact.

If a designer uses ‘unnecessary’ transparencies and animations just because a design tool makes those things easy, that is not a problem with the design tool.

If a tool makes something bad easy it is partially responsible.