Yes, Windows Defender is kind of weak, I agree with that. Now, saying that the new Microsoft Security Essentials is also going to be bad just because Windows Defender is not good either, is in my view a bit premature and unfair to say the least.
You see, unlike this new Security Essentials which was created completely in house and from the ground up by Microsoft programmers, Windows Defender was not really developed by Microsoft from the get-go, so it was never a true Microsoft product like the way the Windows OS's or Office products are.
To make a long story short, Windows Defender is really a non-Microsoft program called "GIANT AntiSpyware", which was originally developed by a Company called "Giant Company software". This company was later bought out by Microsoft, then soon afterwards Microsoft renamed GIANT AntiSpyware in to "Microsoft AntiSpyware". A little later after that, the Microsoft AntiSpyware program was once again renamed in to Windows Defender, which is what it is now. Windows Defender still remains pretty much the same from the original GIANT AntiSpyware program, very little has changed.
So, if there is a lesson here to be learned, don't put your name on a crappy product made by somebody else, or your reputation will suffer for it. So, with all this said, it will be better to just wait and see how this new, 100% Microsoft made from scratch anti-spyware program compares to not just Windows Defender, but also the rest of the anti-spyware crowd out there. After all, the popular word on the web is, the new Windows 7 is actually a pretty good improvement over Vista, and XP too, so it seems that there might actually be some hope here for the new Microsoft Security Essentials.