I wouldn't spent too much time on Char-op because they only really care about outliers. And it's rarely hybrid that breaks things (in some cases, sure). Unless they have a handbook out for it.
I've had 2 hybrid PCs in the game I'm running, and I'm looking to bring in a third shortly. It really comes down to a few things:
Good class features. Some hybrids just get gypped (paladin), while some take almost no penalty to core abilities (swordmage). Mostly for the defender role: they rely on their central class features but those features aren't easy to scale back. Leaders have a very simple core ability that can be scaled back to half in a linear way (their 2/encounter heal), strikers all pretty much play by the same rules (bonus to damage only with class powers). Controllers really lack defining class features and therefore are usually in a pretty good shape as hybrids, they're mainly about power selection.
AC is another issue, you need to choose carefully to not gimp yourself here, OR you need to take a pairing that doesn't really need anything extra from Hybrid Talent so you can get armor (or an armor emulating feature like swordmage warding). Even after that, hybrids are feat-starved as they have access to two classes worth of feats and may need them to get back on par in an area. Good feat selection can help you fall more into one of your two roles (toughness for defenders, for example).
Stats need some overlap, but that's usually pretty clear.
Feat support overlap. Lots of feats are better for certain classes. Since you're going to feel feat-starved anyway you should really look for combos that have a lot of good potential synergy. Look for things like combos that use many powers with the same damage type, make lots of charging attacks, like and have good chances to crit et cetera.
Putting it all together: Swordmage / Artificer is a great combo for example. Swordmages have (IMHO) the strongest hybrid marking mechanic, artifacer don't loose anything key for being a hybrid. Both are happy in leather armor (though you'll want swordmage warding) and you can go Int/Con and have full stat overlap. Both have a mix of implement and weapon powers, and you can use any blade for an implement (you'll want a blade for warding). They both do pretty well with force and thunder powers, which have some nice feat support. On top of that both have controller sub-roles, if you multiclass into wizard you're going to be able to slip between three distinct roles to a fairly wide degree. You'll never beat a generalist but how well you can cover each role is mostly down to how you choose your powers gear and feats.