'They've been trying to impeach Trump since before he was sworn in. If they had the goods they would have begun impeachment hearings instead of this inquiry.'
Yes, they have. So? As for 'impeachment hearings instead of this inquiry' , they're just following procedure-witness testimony before hearings. It appears to me that you want to skip the arraignment process, go directly to trial, skip that, and get a dismissal. That's not how it works. The fact that they're getting testimony lined up before the hearing is not indicative of lack of evidence.
Our President made a couple phone calls to a foreign government and asked them to investigate a private citizen who is running against him. That alone is impeachable and is a textbook example of why impeachment exists. Trump not only admitted he did this-twice-in public, on video but Mulvaney admitted it to the Press and said they do it 'all the time'. The only questions that linger are whether or not Trump wants Biden investigated only because he's a political rival and the reason he held the financial aid back. But even if those weren't loose ends, he committed an impeachable offense twice and admitted to it.