Having to target a disengage skill as a MNK is quite annoying, but being able to dash right towards the enemy as a gap closer, without a risk of overshooting it is handy, not to mention there's certainly people who enjoy Thunderclap being similar to BLM's Aetherial Manipulation. However, by looking to RPR there is a solution to this that allows for best of both worlds.

Keep Thunderclap the way it is and simply give MNK another ability which moves them backwards without interacting with a target, like RPR's Hell's Egress and similarly to it, shares cd/charges with Thunderclap. Even if you'd like to freely move ahead without a target, you can also do that by turning around beforehand. It can even use the same animation, just in reverse, in order to save on assets.