It's not like it would've cost them much to investigate and come up with whatever outcome the US wanted to see. Their problem, of course, was that since the issue was a partisan ploy by one party to hurt the other, going along with it would've hurt them in the near or middle term when the other party got back in power. It's precisely because they are so dependent on American support that they couldn't afford to let themselves be used as a partisan weapon.

Now, before I get into the below, let me clarify my position on impeachment. I can sympathize with the arguments that impeachment should not have happened until all the relevant court cases had run their course - the timeline would've become inconvenient to everyone involved if impeachment had happened in the summer of 2020, but so be it. I can accept the arguments that what Trump did wasn't quite bad enough for impeachment - it is a judgement call in the end. Or even the ones, like Marco Rubio's rather interesting blog post, arguing that impeachment is so politically explosive in today's political landscape that it shouldn't be pursued unless a large majority of the country agrees - although that rather implies that your presidency becomes a sort of temporary dictatorship, with a significant danger of turning into a not-so-temporary one when such an untouchable, all-powerful president declines to relinquish power peacefully when voted out of office. Just look at Turkey. And last but not least, I'm not denying earlier presidents haven't done illegal things as well, which could conceivably have been grounds for impeachment, if they had come out into the open during that presidency.

But this notion that Trump didn't do anything wrong at all, is ludicrous. And it's quite disturbing that he can get away with having his lawyers claim just that. Sure, there are plenty of Republican Senators who, while voting against impeachment, are making clear that he did definitely do something wrong - but they don't dare to make that argument loudly and clearly, openly calling the president out on his bullshit.

Trump's inclination to engage in a 'quid pro quo' is clear, even if he didn't literally use the term, already from that phone transcript. Equally clear is that, out of the many potential cases of corruption in Ukraine, he was only interested in the one that would embarrass a high-profile political opponent. Of course, just because he hinted at that during one call doesn't prove that he went through with it, the call by itself could have been dismissed as inappropriate but ultimately harmless enough. But when you see what happened afterwards, it's clear that the OMB did in fact keep blocking the funds for so long that finally the Pentagon was no longer able to pay them in full before their legal deadline, without ever notifying Congress as it was supposed to do. And also clear that the OMB only released its hold after the issue had become headline news. Whether the OMB did so on explicit orders from Trump, or more based on some indirect understanding, that's indeed not proven, and would require further testimony and/or documentation. It's also not proven whether targeting Biden was the sole purpose of the hold, that's the kind of thing that's impossible to prove - but clearly there was, at least, no other purpose which the White House was willing to state to Congress in order to block the aid in the legal way.

As for your arguments about how people should get themselves elected president if they want to question the president's decision, well, that brings us back to the Rubio argument and the stuff about temporary dictators, who can do basically whatever the hell they want as long as they were legitimately elected. Before too long, they may keep doing whatever the hell they want even after they are legitimately voted out of office - or they just rig the game beforehand so as to ensure they can't be voted out of office.