Designer:
Responzivity looks little off:

I:
1) Yep, by default all elements are excesively large, so i need to do many breaks to fit all scenarios and keep important informations in first few screens.
2) Sometimes you follow 1280 max-width, sometimes 1440, sometimes others. It is hard to achieve some consistent look on smaller devices than your biiig monitor.
3) Design is heavily dependent on large and various images with text overlay. In some scenarios text become unreadable.
4) You did not design a responzive version in first place, so FUCK OFF! I just trying to do my best to fix your shit because you suck as hell!

Escaled quickly, but i'm so tired of this idiot.

I only use two breakpoints. 770, 1200

Deal wiz it

I suggest making the designer supply one sketch per breakpoint. And not implementing anything before you get them

That often makes them realize if there are problems with their design on smaller screens.

If that’s too much: look up the most commonly used device among your audience and make them design for that first, and say ”desktop isn’t as important”

I use no breakpoints at all and everything I do is still fully responsive. Deal with it.

so you have intern designer? from your remarks it seems so! There is a nice intro to digital design (or ui design if you like) for developers who aren't designers and "designers" who are shitty at their work.

It is called refactoring UI, just send him a link to it and tell him to not to send you shitty designs anymore!

A lot of people call themselves designers but in reality not knowing shit about it, just following trends without knowing why is that and why it is better than previous trend. What are caveats of particular approach and what that means for user experience.

Spitting screens from sketch, everybody can do that! Wanna better experience with designer?

Ask it for design guide and be annoying about every single detail, rely on design guide and when something inconsistent pops out in new design you just point to the design guide and ask about where is that new shiny turd designer just produced!