All weapon actions should involve a tradeoff. This would allow martial characters more options, especially at lower levels, while also not stepping on the toes of class/race abilities.
Rush should allow you to move double your remaining movement (costing it in the process) and attack, but all AoOs you provoke are made at advantage against you. And obviously you can only rush in a straight line.
Weakening Strike should take a -5 penalty to hit (or disadvantage), and a successful hit does damage and the target make their next attack at disadvantage.
Crippling Strike should take a -5 penalty to hit, and if hit the target should be allowed a Con ST to move at half speed instead of 0.
(similar and so on for Backbreaker, Flourish, and other weapon actions that deal damage and impose a status effect)
Brace seems balanced-ish: you lose your movement speed (can you move and then brace? If so, it's unbalanced.) to get a bonus to damage. However, this steps on the toes of rogue's "Steady Aim" feature, so it should either also cost a bonus action or be made with a -5 penalty to hit for non-rogues.
Heartstopper should not exist. Don't mess with the action economy Larian. 1 action is not equivalent to 1, 2, or even 3 DOS-action-points. If they really want heartstopper, then it should be made with at disadvantage, deal no damage, and the enemy ALSO gets a Con ST to ignore the effect).
-5 it is a bit too much, it can make it too unprofitable to use it
