You can suspect what you like but merely suspecting that something is true is not "proof" that it is.
Well we've already seen plenty of proof that Trump is a huge liar, so adding a few more lies to the already huge heap of Trump's lies is not much of a stretch at all.
And the whole Trump impeachment inquiry has not proven that Trump told anyone that the Ukraines woud not get the aid unless the Bidens were investigated.
How many times did Trump say, "There was no quid pro quo"? And how many of his own appointees have admitted that there was, in fact, a "quid pro quo"?
Remember Jer, these people who testify are under oath. If they lie under oath, they are subject to prosecution. So, rather than subject themselves to prosecution, Gordon Sondland et al have opted to tell the truth.