No, a handgun is not as effective in killing waves of people as a semi-automatic rifle. The focus is on making it more difficult for people unfit to own a gun to obtain one. In addition, the focus also is on universal background checks, which will make it more difficult for some people who don't need to have a gun to even get a handgun. To paraphrase Joe Biden, just because these proposals won't stop every gun murder doesn't mean that we shouldn't try to do something.
It is basically a response to mass shootings. One-on-one you can kill someone with a handgun, you can kill them with a knife, with a bat, with basically any weapon, and gun control proponents recognize that. In a group situation a gun is what allows a killer to harm not just one or two indivuals but dozens. I don't think a handgun is "as" efective a killing instrument.
Why do you say that a rifle is more effective at killing waves of people? It's easier to grab the barrel of a rifle and wrest it away from a shooter than it is with a handgun, handguns are easier to conceal, you can get high capacity magazines for handguns and easily carry more than one and because rifle bullets travel at such a high velocity they sometimes pass straight through a persons body doing less damage than a handgun. I don't own any guns and I may be wrong, but a handgun seems just as dangerous as a rifle to me.