My instinctive thoughts on the answer to your question, while not of course technical, or even "in the know" is this:
Malware uses so many different vehicles and processes to try to get around our protection and is so changeable in its forms that having different procedures for watching our systems can only increase the chances that some new thing may be caught before it can do any damage. I think of it as another tool that might do the same job, but more efficiently or effectively in certain limited circumstances that I am not qualified to predict. Just like a long-handled screwdriver may be awkward in some situations, but can still get the job done, versus a short-handled screwdriver. Or maybe a monkey-wrench versus a set of box wrenches.
I think I shall spring for the extra PRO protection, if I can find the money, if only to increase my peace of mind. That one extra tool may someday win a battle for me. Besides, PRO offers a couple other "perqs", too. However, if I can't find the extra funds, I shall still feel well protected with the basic protection, especially the Web Shield.