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Nah. The 1st stage vehicle design is optimized for reusability. The staging velocity is much lower than you'd want to minimize fuel use, because that way it can fly back to the launch site easily enough, and fuel is cheap but time and operations complexity is expensive.
The heat shields are what it needs for reentry, and the atmospheric engines are what it needs for controlled landing, and those are what it needs for reusability. You're using the same pointless definition that most rocket design programs have: that "efficient" means "payload divided by fuel mass". But fuel is cheap, and the most meaningful definition of "efficient" is actually "payload divided by cost". If each SLS costs $4B to launch, it could have the highest fuel-efficiency quotient of any rocket ever in history before or since and yet its true efficiency would still be too low to ever be sustainable.
A smaller lander means you need more landers. Approximately one hundred times more landers, if you compare the heaviest thing landed on Mars so far (Perserverence) with Starship payload capacity. Starship is gross overkill for putting a flag and a few footprints on Mars and then never going back, but it's about what you'd want as the minimal scale product for a large base or a small city.
Did you mean TSTO? Part of the genius of the Starship design is the realization that, if you have a reusable two-stage-to-orbit design, you've basically also got a three-stage-to-Mars design, just by refueling the second stage and then using it as the third stage too. So instead of launching your big Mars transfer vehicle via a bigger second stage and a bigger-squared first stage, you can get rid of the "squared" level of scaling and just do more launches.
NASA designs avoided going anywhere near this in part because talking about orbital refueling used to be forbidden there. I'd love to place all the blame on a few folks like the former Senator of Alabama, but really once Congress started treating space as a jobs program, the idea of cutting costs was doomed already, and infighting over which costs were the most uncuttable was just icing on the cake.
This, on the other hand, I can't entirely rule out. It would be incredibly shitty hype for investors, because "we're just going to plow our profits into a program that won't pay off in your lifetime" is an awful spiel for getting your hands on someone's retirement fund, but for employees it's been pretty effective hype, a big part of how they've been getting very talented idealistic young people to work very long hours with otherwise barely-competitive salaries.
I don't see how the math works out for a bait-and-switch at this point, though. Starship development wouldn't make sense as a purely greedy investment unless they really expect it to undercut Falcon 9 internal costs, which means a flight rate on the order of what they're pulling off today with Falcon 9, which means so much tonnage to orbit that they'll be able to continue the Mars side of the program as a loss leader. Even if Musk is secretly planning to pull an "aw, shucks, we're going to want to cash out most of those Starlink profits in our lifetimes after all", or he somehow gets pushed out by someone else who wants to change plans, they'd still want to earmark a dozen launches for Mars every so often just to keep attracting talent.
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