It personally doesn't bother me all that much, especially on ground where a good player and the damage buff from level matching can make up the difference. The day I ragequit or throw a wobbly because a Commander or Lt. Commander entered a mission he has every right to enter is the day I need to stop playing the game.
That said, it's not really fair on a Lt. Commander to have to go into a space mission and take on level 50 enemies. Even with their damage buffed, they still lack the BOff slots. Particularly on something like Blockade where you plain out need Lt. Commander and Commander BOff abilities to effectively protect a freighter. Without them you have one Tac Team, minor heals and maybe TBR1. Two players like that at the one freighter are going to struggle.
But you can't divide them by rank either, because that'll kill the queues at lower levels. The only rank divided content it doesn't take 20+ minutes to get a group at below VA is Mirror Universe, and that's because people use it to power level their way to VA.
I would be interested in knowing whether a middle ground option, namely have two queues, one for Lt to Commander, which spawns level 29/30 enemies, and another from Captain to VA which spawns level 50s, would work. I'm sure Cryptic could check the numbers on it to see would it be viable. Too bad they probably won't come in here and tell us...