What do you mean by "everything goes more smoothly?" What are you "worried" about?
The slow-poke won't be trampled, if that is your concern. There is a lot of pushing and shoving at rope drop amongst those in the front of the pack. Try to enter 5 minutes later, if you're going first thing in the a.m.
If you're worried that they'll push themselves too far, I get it. BTDT. You can suggest a wheelchair/
ECV, but you can't push it or force them to use one. They'll probably refuse the ECV and then have to leave the park early. It isn't that they're trying to ruin your day...they're just trying to be normal. Plus, a lot of people feel that if they CAN go on without a chair, they SHOULD, so they don't take one away from someone who actually NEEDS it. If they don't feel that they're a person who needs it, there is no talking them into one.
And even if they get one, you will find that everyone passes you all the same. Those things slow you down, too.
If you just don't want to be held back by this person, tell them before you go that you won't be touring the park with them.