What’s tricky is that Jesus speaks of “the church” before Pentecost, as though it is something that already exists. See, for example, Matthew 18:17.
It all hinges on the meaning of the word “ekklesia,” which we translate as “church.” At its most basic, it simply means “assembly.”
People have “assembled” in the name of God for millennia ...
But He also speaks of it as something that He would build in the future (Matt. 16:18) ... so that is hardly an argument that is decisive. Esp. in light of the fact that we have already exhausted every occurance of the term "church" in the gospels (only 2, both in Matthew).
I have to go back to the indwelling of the HS as the distinctive mark of the NT believer. "He will be with you ... and will be in you ... forever." That didn't happen until Pentecost.