Suction does not hold your cup in place, your PC and vaginal wall muscles do.
SUCTION is created when a cup is unfolding, and then again when you're trying to remove a cup. And both times, it's a temporary condition that you want to alleviate ASAP.
Hold your hand facing up and squeeze your cup onto your palm. There is suction until the cup fills and opens fully. Once it's open, is there any more suction? No. The same thing happens when you insert your cup and unfold it. There is suction until it fills with air and opens fully. That air has to come from outside your vagina because it's like an empty balloon in there -- no air. Then once the cup is open, there is no more suction -- for the same reason there wasn't when it was sitting open on your palm.
[Edited to remove a controversial statement.]
Once the cup is fully open and in use, it is held in place by your vaginal walls and muscles -- not by suction. Has suction somehow been created since it opened? No, not unless you have somehow squished your cup.
Then during the removal process, you need to "break the seal" at the rim so that suction does not occur. If you don't let air into or above your cup and then you pull on it, what's going to happen? Ouch! The harder you pull, the more suction it will create on your cervix and vaginal walls. To break that suction, you need air. Where does that air come from? Again, from outside your vagina. It's an empty balloon in there, remember? You need to create an air channel. Once you get air into and/or above your cup, then is there any more suction? Not unless you run out of air and create suction again.
So the key to both opening your cup and removing your cup is to get air into it. Those are the only times that suction is created -- and both times, you want to relieve the suction ASAP.