Dragoons need to be buffed...

[Lemon8or]

we can't carry through to Disembowel until we land the rear-attack.

You have to see the whole thing here, not just 1 skill. Sure you have to retry Impulse Drive but that is just 1 hit you have to get into position. Once Impulse is fired off, you're done. Comparing to a boss that spin like a yoyo, a monk would lose on Dragon Kick, Twin Snake and Snap Punch or Bootshine, True Strike and Demolish. I'm not saying Monk doesn't have it better than Dragoon regarding the positional stuffs. I'm saying these facts balance itself out. You guys have a shorter wind-up, mandatory positional moves but lower ceiling compared to Monks with much longer wind-up, non-mandatory positional moves but a bit higher ceiling. The difference isn't even big enough to say hey bring Monk instead of Dragoon cause they do way more DPS. No, that's not the case. And in some cases, the DPS difference is already made up by having a single bard in the party. Monk + Bard is gonna do the same as Dragoon + Bard. Just because the OP disregards that aspect of balance doesn't mean it's not thought out already.

If one had to choose between taking equally skilled/geared DRG or Monk, they would be likely to choose a Monk unless there's a Bard or two, as they can potentially deal more damage, and if the fight is not very favourable for Monks which prevents them from reaching their max DPS

What raid group does NOT have at least one Bard? And as you said "potentially" and "if the fight is not very favourable for monks", that's the trade off. You either do really great in one fight or passable for others. Most Monks will suck compared to Dragoons in primals fights where lots of disconnect happens.

So: Monks: Potentially higher DPS, skills to aid the whole group. DRGs: Somewhat better burst, but lower overall DPS, single skill to aid a Bard with just a 10% damage buff.

To me the gap between seems too big.

The key word is "potentially". And as explained, the extra DPS bard could do should be counted as DRG DPS since without a DRG, that would not be possible to get. So MNK + BRD = DRG + BRD assuming same skills levels and gears.
Good thing the devs don't see it the same way you do.