No, I think you're wrong about this. Yes, tsunamis are "awesome", and "powerful", but that doesn't mean they kill as soon as they touch someone, or smash a person to bits against debris like a tornado, or anything else that would make even an experienced surfer "completely helpless".
The "power" of a tsuami like the one in the photograph is owing to the quantity of water that rushes inland. It's much like a (very deep) flash flood. It's not that it crashes into people like a supersonic freight train. It's just that you cannot resist its flow. You can't stay on your feet, and you can't do much but be carried along with the water.
When the wave reaches a swimmer it's a wall of water going ~20 mph. What matters at the moment of impact is largely that fact, not how fast the wave was going out at sea, how long the gap between peak and trough, and all the rest.
A wall of water moving at ~20mph is definitely survivable. If you dove into that wall, you would to a lot to minimize the impact to yourself. You would be reducing your surface area, and reducing the amount of force transmitted from water to you. So, you would reduce the tumbling that would likely occur down along the sand. Once the turbulent leading edge of the wave passed, you wouldn't be "pushed down into the sand" for minutes at a time. You'd be able to push up from the bottom to the surface.
Now, you'd be right in the middle of a ~20 mph water current, heading inland. There's nothing you can do to fight that current, but you can swim laterally, and perhaps grab onto a tree, or a structure.
So, I think Monday's right. You wouldn't be entirely helpless in the face of a wave like that.
And if you look at the pictures, you can see that even the top of that second wave stacked on the first is no more than about 15'. You can see that by looking at the boats right in front of the second wave. The second wave is no more than 7 or 8' above the water level after the first wave, and maybe a bit less. (How tall are those masts, do you think?) The first wave is about the same height above the floor.
" but that doesn't mean they kill as soon as they touch someone, or smash a person to bits against debris like a tornado"
Stronger people were more likely to survive than the young or old, but I wouldn't like to be caught in the whitewater on the face. That would be a long ride in a washing machine spin cycle. Better to dive under the leading edge and come up behind if the water is deep enough. Even if it did sweep you inland on it's back, so to speak, your chances of survival would be greatly increased.