I personally don't have that evidence, but I'm just another anonymous poster on the internet. There are experts who have studied epidemics, and pandemics for years, and they have compiled a long list of things that should have been done, and Trump's qualified advisors gave him a list of things he should have done at the time. If that's what you are looking for, it's easy to find. He preferred the advice from Fox and Friends, and Hannity over the experts. As usual, Trump would rather go with what he thinks will help him politically over what the experts say. This is similar to when he chose to believe Putin over every expert investigative agency we have. The man is a fool.
I'm no Trump fan, and I don't think he's done a great job during this pandemic, but when you say "a lot fewer people would have died if Trump had done his job" it would be nice to know just what you think he didn't do, how many fewer people would have died, and what you base that belief on. For that matter, it might be important to know just what Trump even has the power to do, depending on what you think he should have done differently.
I'm sure there are things the administration could have done better. There are things various governors could have done better. I know that Cuomo was pretty dismissive of COVID-19 until it started to really hit NY, for example. How many fewer people would have died, though...that's not something I think can be very accurately determined. I don't know what the baselines for comparison would be.