I think another issue is that even if attacks can be avoided, a DD has their DPS affected by having to dodge all the time whereas for the most part BLM and BRD are free to continue unleashing hell on mobs. It might be possible to do content without blm and brd but it's a bit naive to think that it's entirely a community issue and that certain jobs don't experience some pretty harsh penalties.

mnk and drg have some pretty awkward positional combos to use whereas brd and blm have very very simple combos. blm only has to avoid being resisted (which is kind of present in mnk and drg's combos in the form of physical accuracy) in order to combo. brd in order to combo has to just use their first ws more than 8 malms from the target. While it isn't exactly hard to do the mnk and drg positional combos in normal situations, current endgame has mobs moving around a lot and require close range jobs to run out of range a lot, the latter of which hurts DPS without even taking into account combo positioning.