Not quite. Catching a pass with a foot out of bounds means the receiver is out of bounds and the ball is dead (but not out of bounds). The kick never went out of bounds; intuitively it would make more sense to say the ball is dead where it was first touched by the player whose foot is out of bounds.
What if he just drifted over to catch the ball on the fly, and did, but with one foot out of bounds? Would you rule that differently? The league wants the ball kept in bounds on kickoffs, and established a very significant consequence for failing to do so. For whatever reason, that was important to them. Smart players narrow the field a few more feet on each side. That's about all it is.
When the ball is kept in play but the player goes out of play before touching it. I think you're right that there was a reason for it but I don't see the logic of penalizing a team for accurately placing a kickoff near the sideline - but not out of bounds - as a strategy for pinning a team back and helping the coverage team succeed. As you said, the penalty is severe if the ball goes out of bounds, but when it doesn't, the risk-reward should be there.
What would be the difference in the same situation with a punt? If the returner goes out of bounds and fields the ball it's a dead ball at that spot I believe correct?