Harder? Not really. That's an illusion caused by lack of space and less-powerful weapons. The Battle Rifle and Halo's AR fire the same ammo, but it takes twenty-plus rounds to drop a Combat form when it used to take fifteen. The M6C and the M6D are not related, unless it's in the fashion that the M1911 and M9 are in the real world. It used to take a single magazine to kill an Elite. Now it takes one and most of another. Or the Fuel Rod Gun. It used to be damage-equivalent to the rocket launcher, with a single blast being instant doom to a Banshee or Ghost. Now it takes two shots to kill a Ghost, three or four for a Banshee. Don't tell me the weapon power wasn't nerfed, it was.
In truth, you actually tend to engage fewer enemies at once, because you'd never survive taking on as many as you used to in Halo. The most Combat Forms I've ever counted onscreen at once was about ten, most I've ever engaged at once and lived to tell about it was seven. The Flood just don't feel as overwhelming as they used to, a lot of the time they're only in groups of two or four Combat Forms. There's nothing in Halo 2 at all to compare to the wave after wave of Infection Forms that introduced you to the Flood in Halo.
The Needler is the only weapon with which you can reasonably expect to kill anything that walks on two legs (Hunters excepted) in fifteen rounds or less. And without having to stand outside of cover for a long enough time for a bunch of Covies to hose you down with plasma fire. For the Flood, though, I prefer either dual SMGs or a Sentinel Beam. The Flood have a disturbing habit of taking enough needles to cause an explosion, but managing to run up to me before the needles actually explode.
