Thanks for the correction- that's good to know.
However, IMHO, it is a weakness that there are any that do require class features, especially since it mandated a wait for this option to be relased in a subsequent supplement to the game.
I picked ranger to illustrate this because it led to problems with my very first 4Ed PC- at the time, a PHB1 only campaign (since expanded). There may be other Paths for other classes with the same flaw.
Warlock is a tough class to MC into for similar reasons. A lot of the paragon paths modify how your curse works or have powers which key off of it. There are some rather nasty combos which work with other classes going into Warlock PPs, but it takes some thought to get it to work out right.
On a side note, I'll also add that Paragon Multiclassing can actually turn out pretty well with the right combo. You do lose the additional benefit that most PPs grant when spending an action point, but I've found that I don't miss that nearly as much as I thought I would.
I understand why there are people who feel MCing is weak. At first glance, you are 'losing' feats. However, the first feat to break into a class usually carries enough benefit to (IMO) offset that loss. At the very least you get another trained skill, so that actually puts you one feat ahead in a way -skill training + whatever other benefit you get. With one power swap feat, you're about even (if you don't considered that some powers are a lot more powerful when combined with class features from certain classes.) You would need to take 3 more feats to PMC, so you end up being down 2. Still, that being said, there are some powers which combine with certain class features to create something pretty potent.
Even if you completely hate MCing in 4E, I see no reason to not at least take the first feat for a class. As said, you get training in a new skill in addition to other benefits. Also, as the OP pointed out, MCing into a leader class grants you a once per day ability to heal. It never hurts to have some back up healing for when an encounter goes south.