100% agree. The way some people talk you'd think he'd asked a 6ft 7 target man to play left back, rather than trying to give a player who likes to run at people and get in behind the opportunity to better utilise their skills, in a position which isn't completely unfamiliar to them. It didn't work, but it was a perfectly logical thing to do.
If he wanted to give him a try with DCL, which I am all for, then why not try that then, instead of forcing him into system?
He may be quick, and your striker to left back is an extreme example, but just that change of position can be a huge change depending on the player and the plan. If it was that easy, most centre halves would be decent fullbacks and vice versa. Most centre mids would be lost as a winger, and same applies the other way. Some players are negatively effected from changing between a 2 and a 3, playing the same basic position.
He's a young lad, and it's not the be all and end all if he's not fully up to speed, but all people ask is for a bit of consistency in approach. I mean, in 1 of our last games, I can't remember if it was spurs or not, he brought Kean on for Walcott. But kept Richarlison, who Silva has insisted is best playing off the right, in the centre, and left Kean on the wing. Now you could argue why make 2 changes instead of 1, but that's exactly what he did when he replaced Michael Keane with Mason Holgate, and switched Yerry Mina from the left to right, and Holgate, a right sided CB, to play on the left.
If we had a system that was fool proof, a team winning and full of confidence, and excellent team chemistry, I could understand putting Kean in any position, for minutes, experience, confidence boosts, etc, and players undoubtedly love playing anywhere they can when the positivity is flowing in that way. But we're not, and it seems crazy to me to do that in the situation we are in.