Not an expert in any of that, but I think overall impact may be greater if people with sufficient means take a more hands-on approach that grants visibility of where money is going. I lean environmentalist be the truth is that there’s a good deal of well-marketed snake oil in the environmental space.
The issue with quibbling over impact is my experience is that people end up doing neither. I recently started a Master's in ecology so I don't have a good idea of what's cost effective right now but I know the field is pretty shockingly underfunded (both for general research and conservation projects). I learned the "fun" fact recently that bird populations in the US are down ~30% in the last 55 years.
A fair assessment. Doing nothing is not the answer to the risk of doing the wrong thing. It's probably worth some time spent on due diligence when selecting groups to donate to, regardless.