I agree that everything moves too fast for that Battletech feeling and for realism. However, PGI has made a game where they want all mechs to be roughly equal. In other words, while a Dire Wolf may be able to take on five Firestarters single-handedly in lore and in TT, this cannot be the case in MWO. For this reason, you simply cannot make light mechs any slower, because it becomes too easy for everyone else to hit them and smash them instantly. Especially after the rescale, now that 35 tonners are huge glass cannons / paper tigers. If you decrease agility equally across the board, it will hurt the light mechs far more than the heavier mechs.
I also think the idea that horsepower = agility & speed is a load of crap. You have to take into consideration that physics don't work the same way for a 100 ton battlemech as a 100 kilogram person or a 100 gram lizard.
![Posted Image](https://media.giphy.com/media/n98X80NYxTqmI/200.gif)
As you scale up, the effect seen above cannot be replicated. The fastest man alive isn't able to run on water, and there is no chance of designing human-sized androids that can actually run on water either. Because physics change from a micro scale to a macro scale. For example, a 100 ton Kodiak trying to make a U-turn in sand while going at 70 kph is going to have a hard time. Because when it plants one foot and places all of 100 tons of weight on that foot, it's going to respond differently than when a 20 ton mech does it, or a person does it, or a small reptile does it. You can't just scale everything up and expect everything to handle identically.
Also, I find it rather dumb to have torso twist so heavily related to the power of the fusion engine, when that sort of thing would realistically be much more dependent on the structure, actuators and myomers. Yes, the engine powers everything, but a bigger engine wouldn't make everything go faster, necessarily.
TL;DR - It makes no sense for agility to be so heavily related to engine rating. Heavy mechs and assault mechs need to be a lot more clumsy and cumbersome, especially the mechs with high engine rating. Being able to go fast does not necessarily equal insane acceleration (due to the unstable surfaces) or insane agility.
The game would benefit greatly if there was an agility nerf to heavies and assaults with a high engine rating. And for God's sake, lose some of those crazy agility quirks.