We can't be so sure. The probes have discovered that Mars has no channels and vegetation. That water is uncommon (then discovered that it is still there in some quantity). They found out precise atmospheric composition, mapped out all major surface features, observed the climate over decades. They discovered perchlorate toxicity of the soil for humans, something that would have been a nasty surprise to a manned crew.
Am not opposed to Mars expeditions in principle, it's an exciting thought. But I just can't see humans contributing all that much on the odd few landings, with a high chance of contaminating whatever traces of life there could be.
Of course though you're completely right that mapping out the rough surface and climatic patterns is critical, but that would have been capable with the first probe to Mars - launched some 53 years ago. There's just really extreme diminishing returns with probes and rovers. For instance these [1] are NASA's highlights for what Perseverance, the latest Mars rover, has achieved in 4 years. To call them uninspiring would be an understatement.
[1] - https://science.nasa.gov/mission/mars-2020-perseverance/scie...
https://www.investmets.com/nasa-workshops-aim-to-merge-on-an...