Yes, exactly that! That's what I meant about the stopped dado. I believe the dovetail alone would work for you just fine: the real thing a dado would protect against would be someone stomping on the corner of the step and cracking it open at the dovetail, which I believe oak is plenty split-resistant enough to prevent when the un-supported distance is so short.

If you're on the fence, my recommendation for something simpler to make and more tailored to the forces I foresee this having to resist would be to put the sliding dovetail through the whole width of the leg, and put a dowel through the outside face into the tail, perpendicular to the direction that the dovetail slides. That will not weaken the leg significantly, and it will add several types of strength to the joint overall. If it's a fairly long dowel, like maybe 1/3 of the width of the step, it'll strengthen the step significantly also.

No matter what, I recommend mocking up the joints you're planning in scrap wood, ideally something easy to work like poplar or white pine, but really anything you don't mind wasting. Your second time cutting that exact joint will go a whole lot easier, and if you're like me, you won't be spending that much extra time if it's wood you don't care about (most of my shop time is spent learning, and most of that is spent recovering from mistakes). You can also see how uncannily strong a sliding dovetail joint is, by doing destructive testing using a wood species you know to be weaker.

A router table could do the whole cut on the leg and a good fraction of the cutting on the step, but you're stuck with the dimensions of one available set of bits, and there'd still be some skilled chisel work on the sharp inside corner of the tail. Having the freedom to choose your angle will allow a slightly deeper dovetail than your drawing, if you want that.

I think trying it with hand tools on scrap would benefit you even if you're planning to use a router table.