So, it’s good to keep in mind you will face that, and be prepared with some patience and counter-arguments.

I wouldn't really encourage this, as much as one may be inclined. Some may be willing to change their mind, but many others of a resistant disposition aren't that interested in leaving so much as venting frustrations, and lurkers may get the impression the alternative you're advocating is full of however you may present yourself in your argument.

It's better to look for those genuinely asking where to move to or what alternatives there are, and if they specifically mention Lemmy, then you might help them along there. Otherwise I'd suggest mentioning a variety of alternatives to choose from and mix together, such as setting up a RSS reader (if they're more of a passive reader), Lemmy or Kbin/Mbin, or scaling back Reddit use as they explore these alternatives, rather than pressing them to drop it outright for a single option.