As valid as your opinion is, please don't try to make it out as evidence. There is absolutely no evidence Laporte and Koulibaly would survive everywhere, it's a pretty silly statement. If the other 9 players aren't on their game, they would be exposed just like any other CB you care to name in that situation.
You also state anything other than Laporte and Koulibaly would get rings run around them at Barcelona, Madrid etc. Well Otamendi and Fernandinho for 2/3rds of the game survived pretty well in Madrid, in the main because our work rate from the forwards and midfield was so high and protected them brilliantly.
There's far more to it than just CB's. Although you do make a very good point with the price, if we can get Koulibaly for £45m, then it reduces the risk a lot and might just sway the balance of opinion, personally I would find it somewhat understandable even though my personal preference would still be Garcia, Tosin, THB with Fern as the proven option if they struggle.