I'd say it's much more than that. It's a argument that he probably did say it.
My argument that when the totality of evidence is considered collectively, which includes many of the other things that Trump has said and done revealing similar selfish, malevolent, and disloyal thinking, as well as a growing list of anonymous sources and news outlets vetting them, and the deafening silence of all but Trump's apologists, the charges are very credible. That indicates more than "could have." It says to me and millions of others that he probably did say it.
And isn't that what matters? It's why Trump is receiving so much blow back even from former Trump supporters that have only recently abandoned him. People hear the words "sucker" and "loser" and find them very consistent with the rest of Trump's thinking and values.
I see this scandal as one with traction that will deepen and continue to haunt Trump through the election. It doesn't even matter in 2020 America what Trump said. It's enough that the charges are coming from multiple directions and that they are credible. Even if the whole thing was a hoax and a conspiracy, it's fixed in people's minds now. It worked, and it worked because true or not, it's credible.
I don't believe that for a moment, but even if true, Trump set himself up to be dealt with like that, like somebody who is heard saying, "I'm going to kill you," and then gets framed for murder by somebody who heard the comment and wants the recipient of the threat dead. One's mouth can make false charges seem credible. If that's what's going on here, Trump has only himself to blame for making himself vulnerable in this manner.