I have been on multiple lines and would not do Royal Caribbean again. They were my least favorite in Alaska I am guessing they are cheapest because they don't go there.
Glacier Bay via air is definitely a different site than via ship. Both good but different.
Princess and Holland are the most popular and there is a reason for it.
I also agree with Hubbard being missed frequently in May. So is Tracy Arm. Glacier Bay makes the most sense. Expand your horizons and look at other lines.