Hey... I know this is a fairly old post. But I think I just solved at least my version of this issue.
I was simply trying to create a Facebook banner (820px x 312px). Simple high res background, my transparent vector logo, and a few lines of simple text. Every time I would go to export, no matter what format I tried, no matter what I changed regarding the DPI, etc., my text and logo was always pixelated and super unprofessional.
After reading on here that it may have had something to do with me using my 2015 MacBook Pro 15" Retina, I started looking for any and all Retina-themed options/toggles. I found one that did the trick.
In Export Persona, Slices, Export Preset, choose "Retina PNG-24" (instead of "Single PNG-24").
This resulted in two options for exported files, I chose the "x2" option, and now my image looks beautifully crisp and perfect. I did not have to rasterize anything or convert anything in the design itself.
I believe this is a similar fix to one I saw earlier in this thread, advising to bump things up to a 200% view, but I didn't want to redesign anything, and now this is working perfectly. Not sure if you can tell a difference in these graphics (depending on what kind of screen you're viewing on), but I SURE can; and I am very happy to have found an easy solution to this.
Hope this helps anyone who may be struggling with the same issue I had.
Cheers!
