Thanks for the feedback (I'm one of the Overleaf founders). Just to address a few of your points:

1) You can choose a pdf preview, which is much sharper -- it's currently in beta which is why it's not the default, but you can choose it via the settings menu (click the gear icon in the top right in the editor)

2) You can jump both ways in Overleaf too -- right click on some text in the editor and choose "position in preview"

3) You can choose from a number of different LaTeX engines and keybindings on Overleaf too -- again, via the settings menu in the editor.

Hope this helps, and thanks again for the feedback.