I'm sorry but pressing 123 is no more difficult than pressing 111. There is no more skill involved in either set, you are literally performing the same action only over a slightly different surface area. If your idea of greater skill is more buttons than you really don't have any skill at all. From a practical standpoint if there is no benefit to using any of the individual skills a combo individually than there is no reason to have those skills on separate keys. Note the IF, because that should be the defining factor not some imagined skill level to make people feel more l33t.

You can add whatever ridiculous level of hyperbole you want to put on it, but that doesn't change the fact, once a person has assigned a key to an ability and learned where that ability is, there is no skill involved in pressing those keys in order.

You want to want to add complexity add OGCD abilities that are reliant on fights and mechanics so that you have to think about when and where to use an ability. It's players thinking that using combo's denotes skill that leads to lazy players who are unable to improve and adapt and think pressing 1'2'3 and avoiding aoes means they are playing well.