While I agree with the overall thrust of your point, I think it's a bit unfair to the original commenter.
Like it all depends on exactly what the "this" is they are referring to. I mean there are few different questions on the table here:
1) Can we ensure that the overall gap between the amount of money the most successful people have and the least successful people remains relatively low.
Yes, ofc we can. We can impose taxes and create UBI.
2) Can we make sure that there is a strong middle class, i.e., that the income distribution is bell shaped rather than two humped.
Here, I agree that there isn't much we can do about this. We can use taxes to make sure that the top and bottom humps aren't too far apart (e.g. top 1% only make 20% of the income not 90%) but the shape of the distribution is entirely determined by productivity/demand facts that are almost entirely outside of our control.
I mean, in a world in which the amount of profit your skills generate for the company is two humped you'll end up with a two-humped distribution of wealth/income no matter how much you tax. At least unless you are willing to unfairly and randomly select some people and give them more money than others.
And it's not at all clear we can avoid this by making sure that everyone has access to a great education and the like. In any number of jobs there are just non-linear returns to ability that heavily favor the top earners. For instance, sports (and similarly with acting/youtubing etc..) has the property that the best athletes get paid way way more than those who aren't good enough to make it onto a pro-team. The same is true with programming since there are massive returns to scale (and because coordination is hard hiring more slightly worse programmers isn't as good).
So there is a real chance we may move to a society without much middle class as we transition to more and more intellectual work and automate more. I don't know. But I don't actually believe that it's a problem.
What matters isn't whether there are people in the middle of the income distribution. What matters is that there isn't too big a difference between the top and the bottom.