Ok, suppose the current standard treatment is A. You have a new treatment B that is 100x cheaper than B, and doesn't trigger allergic reactions that some people have to A. You test against A, and the B group has slightly worse outcomes overall than A. Does that mean that B is useless? What if it is almost as effective, but it's lower cost means more people would be able to use it?
"better" is not a total order, one treatment may be better in some ways and worse in other ways. Especially if you include things like cost and availability.
Even if that's the case, the metric you're interested in isn't "is Treatment B better than doing nothing"; it's "how effective is Treatment B relative to Treatment A". And the most effective way to determine that will be to trial them against each other, not against a placebo.
Ideally, for getting good information, you compare to both. Because you also want to know if your treatment is more effective than a placebo.
You just discovered the entire scientific field of cost-effectiveness.
Wouldn’t those factors be detected and reported on in the trial?