Well that's not true at least for vim.
: read !FOO
will run the FOO command and read the results back into the current buffer. I usually search my codebase by reading the results of a grep into a temporary buffer and 'gf'ing to the appropriate file
Recent versions of evil have the option of choosing undo backend, and I have found the new buildin one impeccable thus far.
I used to do that too, I now use the Ack plugin which is almost instantaneous on a codebase that grep used to take 2s-3s long to search. The speed isn't what matters though, it's the fact that Ack only searches source code, not all files so my results is less polluted with irrelevant matches.