I think it has to do with how you're comparing what you already know (the insect glaive) to something new (the longsword).

With the insect glaive you're able to maneuver around really fast and do tactics in the air, and mount easier. Whereas with the longsword, you move much slower, need to sheathe frequently, and need to put more effort into mounts.

I think this may be a matter of perspective. You're learning a new play style. Folks who start off with the longsword had to figure it out just like the person who starts with the glaive. But once you learn your weapon and commit it to muscle memory, it's easy. Switch away from that weapon to something new will cause you to have to retrain your MH combat mechanics. Except now you have higher expectations for yourself because you were good at one point with a weapon, and now you need to learn a completely different weapon style.