Great score!
I haven't tried other cups but have used diva cup for ~3yrs, started at size 2. Yup, it often feels very snug, and at times when I was just learning it was hard to remove. However, I haven't had problems with leaking or consistent discomfort. I can only think that yours might be positioned a little low?? Try putting it higher, but obviously make sure you can reach the gripper, and definitely turn it so that it opens fully and seals the passage. (*TMI* to remove, I tend to bear down in order to get a good grip, then completely relax my muscles in order to pull it out gently). It does get easier with practice because your muscles learn not to protest and tense up!
No problem using a water-based lube to help insert. And yes, I think I do wait until I've got a true flow, and don't use it on really light days. I wear a liner every day of my cycle anyway and this is usually enough.
HTH.