My original point was I don’t think it’s a red, personally. However I just don’t think it’s a ‘this shows VAR will never work’ moment. The laws (as you’ve just shown in your comment) are to vague and with everything slowed down, every microsecond in analysed.If the officials think he's putting his opponent into a dangerous situation (is he completely in control of his body and does he know exactly where he'll be when he goes out? Also, is his knee locked or is it bent to allow flexibility) than he's guilty of a reckless tackle. There's no one answer, just a set of questions the officials consider each time to come up with the most appropriate response possible.
More precise guidance in the rules needed when things looked at it slow mo for me