Of course their influence looks washed out if all you look at is then and now and not the paths that lead from there to here. It's easy to say bands today are so different than the Beatles, so the Beatles influence is lost. It's just a point that is easy to shoot holes in, since it has only 2 data points.

Look at what pop/rock music was prior to the Beatles and look at what it's been since. Look at the path of bands that is in-between the Beatles and Metallica, not just the end points.
I doubt Metallica could be Metallica in the 50's or 60's. Our culture went ballistic when John Lennon compared the Beatles' popularity to that of Jesus. I think that, and the subsequent cultural cool down, was a necessary precursor to Metallica... but totally talking out my ass, there.


You say there's a huge variety among 4 person guitar-based pop/rock bands, but I suggest the following:
The sound produced by 4 people in a group, 3 with guitars and 1 with a drum set, is totally distinct from all other sounds produced by any group of 4 people w/o any guitars or drum sets (allowing for recordings and synthesizers).