Don't confuse something that's second nature to you to mean that it doesn't add complexity. If it were really that easy, you wouldn't see so many terrible DRGs that rarely have the buff up. It's just one more example of the difference in world view between the good players and the bad. "That DRG must be lazy." "That DRG just doesn't care." "That DRG is looking for a carry." That's not it at all - that DRG WANTS to be good, but literally has trouble doing something that seems to you should be as easy as walking and chewing gum at the same time.
It's very much like the kind of view that makes me shake my head whenever someone says, "Man, this Savage Raid / Ex Trial is so easy ANYONE can do it." They seriously have no idea just how terrible the bulk of players in this game are. For ANY Savage Raid or Ex Trial, and I do mean ANY, you're going to have more folks that have trouble clearing it than are capable of clearing it. Folks with this world view simply don't understand how anyone could be so bad - and so they accuse them of being lazy, instead.
It's fine to think that mechanics like this are annoying or boring. It's fine to consider them to be an irritating chore that you need to perform to keep your DPS up to snuff. Just keep in mind that there are folks out there who are PROUD of the fact that they can manage to press this button every 15-20 seconds while still doing other DRG things - and a whole lot more of them than you might think. Quite likely a majority of DRGs, in fact, given how few people seem capable of clearing endgame content. For these folks Heavy Thrust helps make the job a lot more exciting.
Adding the damage boost to Impulse Drive would be pretty much equivalent to giving a DRG a Job Trait that increases damage by 15%. SE wants to make DRGs do SOMETHING to earn that 15%, even if it's something as simple as keeping an eye on the buff and mashing a single button.