The stakes at trial are "higher" for the defendant, than the stakes in everyday life - so getting it right is more important.
If evidence isn't limited somehow, trials would be overwhelmed with BS witnesses. Here, Congress can pick and choose witnesses by name, and as a general rule, Congress is NOT concerned with getting it right, rather just with obtaining power.
Hearsay is a generally an excellent way to limit evidence and get to the truth. I'm sure there are cases where all the direct witnesses are liars and a hearsay witness is honest, and more likely to result in the right outcome. All rules have exceptions.
The winner of the argument is the side that frames the issue, poses the question. The DEMs have so far been successful at posing the question as an assertion that Hunter Biden's involvement in Burisma has no element of corruption - that is a settled fact in the DEM framing.
Point being that the reliability of evidence isn't the only important aspect to getting a just outcome.
A final thought about hearsay. Should hearsay to the benefit of Trump be admitted?
While that is how they've framed it, I'm not at all sure that it is accepted as true by most people. Real hard to slough off as nothing the Veep's son getting paid millions by the Ukrainian, then Biden bragging about getting a Ukrainian prosecutor fired.
A final thought about hearsay. Should hearsay to the benefit of Trump be admitted?
Generally, I think yes. But I think that should depend on the source and particular circumstances. I doubt the House will let it happen -- hearsay is a one-way street for them. But McConnell might.