

Colonizing the bottom of the ocean would be orders of magnitude easier. Or the South Pole. Or Kīlauea’s open lava pit.
While it is true that you have different sets of problems to solve, nope, they are only cheaper to get to, not necessary easier to colonize, except maybe the South Pole where you just need to build something that only need to withstand the cold, which is easy enough and you could go outside without a space suite or something similar.
The problem with colonizing Mars is the cost, which have as a consequence the cost of everything you send to that place.
But in the end I think that we already have all the basic blocks for a base on Mars (or the Moon) and what it is stopping us is the cost of putting everything together and send it.
We already know how to build isolated environments that can must stay sealed for month or years (subs and International Space Station), we already know how to recycle things like air and water, we already know how to produce vegetables in cramped spaces and with low or no exposure to the sun (think of every weed farm inside houses ;-) ) and minimal water needs, we already know how to develop and deploy complex industrial control systems and so on.
None. But without Tesla you would not have neither all the other models from other car companies. Tesla just started it and demostrated that it is possible to produce an electric car with a decent look (and better that some ICE cars in my opinion) at a time when most of the electric cars done by other company were just some ugly proof of concept (excluding a very few cases) to show at this or that event.
And I read somewhere that what Musk wanted from Tesla was to set the stage, as far as I remember he said that it was ok if Tesla bankrupt after setting the stage.
Considering that everyone else was not able to do even that, I would not call SpaceX a failure. And it is not that NASA did not have its fair number or launch failures, tbh.
You talk about beyond low earth orbit like something way harder, but it not really true. SpaceX put a Tesla in a orbit beyond Mars with a Falcon heavy some years ago, and they still have (and use) the Falcon Heavy.
True but they were trying to launch a rocket that nobody else even tried to build. I would say it is fair that they make some mistakes.