So, the Democrats have insufficient evidence because much of it is in documents not provided, or with witnesses who have not been called. The Democrats infer evidence, even though they don't have it. They did get some phone records, but need to interview those on the calls.
Curiously, the Republican witness on impeachment is one that advised that Congress had the right to have McGann as a witness, and should go to court (where they won). That witness believes (as the Democrats do) that the president is likely guilt of Abuse of Power (quid pro quo, and asking a foreign government to help his campaign). He doesn't believe the Democrats new definition of bribery (since there is case law that defines it differently). The president isn'y yet guilty of Obstruction Of Congress since the issue has not been decided in court.
So, the Republican witness indicated that Congress CANNOT alone decide whether the president had the right to withhold witnesses or documents. Congress is usurping the role of the Courts. Congress should submit an appeal to the courts, which they would almost assuredly win, at least in part. Nixon was guilty of Obstruction of Congress, primarily because the Supreme Court had ruled in the favor of Congress.
BOTTOM LINE
Perhaps the Democrats have proven that Trump asked the president of Ukraine for help in the 2020 election, through Giuliani and directly.
The rest is lacking evidence.
Congress is rightly fighting with the president with regard to the balance of power between the Congress and the Executive Branch. This battle SHOULD NOT be won by the Congress bypassing the courts. In any case, the situation cannot help the Democrats in the 2020 election.
AS AN ASIDE
The lawyers and witnesses did well. The congressmen and women didn't acquit themselves very well (as expected).