The only thing Hybrid keeps in check is that nothing you do will be viable. I do have a solid understanding of what abilities go well with each other. That's why they are taking nerfs in order to make this idea work. And looking for someone who fights as well as a fighter and dealing damage like a rogue is NOT EVEN CLOSE to accurate. Why? You still don't get a fighters marks and or abilities. You don't get the great rogue abilities and damage, you're still getting your bard abilties. You already are spending many feats just to do okay instead of playing that class. You haven't helped anything besides pretend that 4E's implements are perfect.
You say it would be unbalanced, then give ideas to make it balanced instead of saying "Well it is what it is" it's just an idea.
And again, Hybrids aren't good at anything they do. They do NOT complement each other because you have to use abilities that don't work on the other class specific attacks. In a game where it was made for combat, they made you worse at exactly that.
This whole thing is just the start of an idea. What is implemented does not make Bards what they are at all. The Jack of all Trades is a Jack of buffing and healing. How ironic is that? Jack of nothing is what the Bard has become.
They separated the Hybrid's bonuses for a reason; it's far too easy to create the uber-character, that could single handedly reduce a solo to dust. It balances against the ability to go nova, once per encounter, that multi-classed characters can frequently manage.
Once per encounter, for a really heavy hit, or all day, for an incrementally better one.
You've got options already, that aren't game breaking. Bard, with Warlock and Rogue multi. Bard, with Swordmage multi. Paragon multi-classing. Half Elf dilettante power. To pack all of the goodness you want, into one class, is just too much.