counting chickens before the eggs even got laid
No, it's not. Nobody can ever be certain of how a particular justice will rule when they are first placed on the court.
Trump made a promise -- "If elected, my first nominee will be someone from this list," and it was a list prepared largely with input from the Federalist Society, and which was openly available for vetting and comment for months. The general consensus among virtually everyone on the right was that everyone on the list would be a solid pick.
And he fulfilled that promiseIf you don't like who he picked, that's your business. But the guy did exactly what he said he would do on this issue, and if Gorsuch goes nutty, it won't be Trump's fault. He sought advice from the most reliably conservative legal organization there is, and followed it.