So you say the first thing, then you say the second thing. If you think the point of TS% is to say who's better or who's more helpful, then you aren't interpreting it correctly. Is it possible for a dude who mainly dunks to be more efficient than a good three-point shooter? yes. Tyson Chandler in his prime was arguably the most efficient player of the modern era. That doesn't make him a better player or even a better helpful player than Steph, but it doesn't have to.
There is not a "big enough sample" it can always be bigger. So as you include other players and seasons, the distribution will become normalized, and the average will approach the mean. Therefore, you will eventually get to the .44 coefficient, which will make TS% near-perfect. Some players may be aberrations, but that won't be a big enough number to skew the usefulness of the stat. You can make it more accurate for a player by moving the .44 coefficient toward .5 if they had mostly shooting fouls and toward 0 if they have more and-1s and Ts, but you don't really have to worry about that in the grand scheme. It evens out.
Since when is it the burden of TS% to show consistency? Or to show how defenses respond to the misses? There can be other stats for that. It would be like blaming blocks for not showing how far away from the basket a player was when they are blocked. Like who cares? That's for other stats to determine. I'm not saying you aren't asking for good data, but I am saying you shouldn't judge a basic stat like TS% for not being an advanced stat.
Yes, though, sample size does limit variance. That's a fundamental law of statistics, not my opinion.
It tells you exactly what it's supposed to tell you, and it doesn't tell you what it's not supposed to tell you. If you want gravel, beat a stone. If you want water, go to the river. Don't be mad at the stone because you're thirsty.