It does seem to be a problem, having the same characters staying with a ship for decades and not letting them advance further. Look at the TOS crew, you would have thought that after at least three decades of service the likes of Uhura and Chekov would have been given their own commands as well.
I know that the Enterprise
is always going to be a sought after posting, but it should be a rung on someones career ladder to help them get higher faster, not a plateau where they dwell for years before finally moving on.
In TNG, when they were having difficulty with developing/doing anything more with Riker, they had an automatic out with him. Give him his own ship, that way he can return for the odd guest appearance without killing him off.