Light on resources is good but come on we now have 4c/ 8t, 6c/ 12t, 8 /16, 16/32....32/64... processing Power and most have 16Gb ram if not 32...my point is they are concentrating on the wrong thing... sacrificing the most important thing " prevention and protection" .
I doubt many people have 32GB of RAM. I've got 12GB in my main computer (and less in all my others) and for the average user, 8GB is more than enough, unless they have many browser tabs open at once. In any case, lightness is not related to high CPU and/or disk usage, and not RAM usage.
Webroot's poor performance against malware, is not because its light. It is because its signatures and its behaviour blocking are not so good. They could improve both, while still being light.