It looks like your site is running through a varnish accelerator of some kind - is it acting as a CDN as well? That is a common case for making the TTFB appear slower than WebPagetest thinks it should be because it is connecting very quickly to the CDN edge node but that then needs to connect back to the actual server and that all shows up in the TTFB time.
260ms for the actual request time is not too shabby and I wouldn’t worry about it.
Yikes - don’t remove the ads just for the grades. You can see how the visual performance matches up with and without the ads to see what the real impact is but getting all A’s doesn’t really buy you anything in and of itself.