It’s important to note that Pinnacle is DEFINITELY not a 1:1 remake of Ascension. If it was, it would play better… Weapon spawns, etc, aside, there are quite a few differences. First of all, the two towers are much smaller. The “main” tower has had its back nook removed, the problem being that that was a fun spot to swipe a Banshee, a Sniper, and fly up to and snipe in Halo 2. No more. Also, the “wall” behind the sniper nest is now too easily reachable.
Second, quite a few of the walkways were made either more narrow or more broad. A minor change, but a notable one. Also, the on-the-bridge powerup has been removed, along with the Banshee. That makes one entire section of the map completely useless; a waste of space. Also, the center bowl of the map was more of a bowl. In Reach, you can traverse or see over it fine. In Halo 2, you had to jump over the edge or already have the momentum to go from bowl to grass, and it actually somewhat aided in breaking a pursuer’s sightline (you couldn’t see from sniper tower to other side of the bowl if you crouched in the right spot).
All this said, the reason why you hate it is that it frequently devolves into sniper/DMR fights between towers, except that one side of the map gets a Sniper, Rockets, and a Shotgun, while the other only gets a further-away-than-the-other-side Sniper. In Halo 2 the Banshee added a large dynamic and there was reason to use that side of the map, but it’s simply just there now; doesn’t even provide good cover or bottleneck opportunities. It’s a shame, really. It’s not to do with Reach’s gameplay, just how poorly Bungie remade the map.