I agree with you to a point. Certainly, the wanderer system needs work and how people are added to it isn't working well. The changes suggested would need to be standard for every character in the game and I'm not sure that can be done. For example, if a wanderer is at your extreme diplomatic range and marries someone a little further away while you're scheming to befriend them (or any other scheme), I'm sure you wouldn't suggest they couldn't move to the court of their new spouse just because you're scheming against them. But if they just wanted to go somewhere they thought would let them get their claim pressed, then you'd suggest holding them in place. I don't think it's good to have two different rules in place. If someone is already your friend, then I could see them sticking around longer depending on your scheme, but if not, then what reason should they if they think they found a better place to be?
Even with romancing someone, depending on what they are hoping to gain by moving somewhere, that might not be enough to hold them. After all, you haven't yet succeeded in romancing them and may not. For example, if someone had the chance to be romanced by you or to have their claim pressed and gain a title, which do you think is more likely to interest them? On the other hand, if they don't have any claims and are just looking to become a knight, then romancing might be of more interest to them. A dynamic system that makes sense based on a combination of factors - why they are moving, what the scheme is, what their opinion of you is, etc. - would be a great improvement, but I just don't think forcing someone to stick around just so you can complete a scheme against them (if you aren't successful, you could conceivably continue scheming against them for years) is a better option than what we already have. If nothing else, the schemes should definitely stop if they leave diplomatic range as we both see to agree on. But I also agree that improvements need made. I would just like improvements that are believable instead of just a flat lock on movement.