This is completely wrong logic. Low RAM utilization only makes an application slower. Granted we might be talking about 1 second or less slower usually, but it can be higher sometimes.It is a good design of AV to efficiently use limited RAM, not a drawback; I would trust well-engineered AV for my protection more than a one which cannot utilize RAM in an economic way.
I have 3rd party security solution installed, and yet Microsoft forces MalwareDefender to run in the background and consume RAM. I don't care about the RAM usage because it does not matter.
No matter what the memory "efficiency" is, what matters is detection and blocking the execution of malicious code. In that regard, Emsisoft will beat the pants off MalwareDefender. There will something like a 5% or greater difference in Emsisoft's favor and that is very significant nowadays.

