Two big issues with that. First, the arm would have to grab an attachment point of some sort, so you'd be trying to position the rocket and the hand close toget

Two big issues with that. First, the arm would have to grab an attachment point of some sort, so you'd be trying to position the rocket and the hand close together and still enough to lock on. That's a much smaller and tougher target than landing. Second, there's no way you could build a robotic arm and grasping mechanism that's strong enough to hold the rocket once the engine shuts down, while also being nimble enough to reach out and grab it. To even have a chance, you'd need three arms and three attachment points, evenly spaced around the rocket, and coordinated to all grab on at the same time. This sort of thing works well in space when everything is just kind of floating next to each other, and you only have to deal with very small thrusts to make small position adjustments, and momentum when you try to move things. (Weightless != massless) But down on the surface everything that's not solidly on the ground is constantly accelerating towards the center of the planet, and it takes a lot of force to counter-act that.