It doesn't necessarily work better. They get more DPS out of it yes, but the opportunities to actually use it are much less frequent. Stormtroopers can hide anywhere and catch retreating squads or ambush squads in general with maximum close range DPS using the ability. It isn't as strong on them pure DPS-wise, but they can usually use it more often and more effectively.
SMG paras and ST are used differently.
Tactical movement is a good ability, I am simply pointing out that it was design for Paras and they benefit more as Brick Top claimed.
Now if one want to talk about ambush there is little reason to compare Paras and ST. One should compare Commandos and ST.
Commandos get a grenade for more Alpha damage and speed boost (with veterancy) for ambush bonus allowing them chase to get wipes also.
One has to also point out the danger in using tactical movement, if thing go sour the penalties speed and target size remain even if one retreats.
All and all the ability is not bad but it certainly stronger when they had ST44 as Brick Top claimed.