While the Wikipedia page I assume you are pulling that $3 million figure for both films says it was accessed in 2018, if you look at the actual underlying page: https://www.the-numbers.com/movie/Superman-Unbound#more
it is clear that the financials are from 2013. I forget where the source is, but for the Wonder Woman movie, about a year ago, there was this entire discussion (right before the DC Films live action was released) were folks were arguing that it was going to flop, and partially basing their 'facts' on the fact that the WW solo made so little, they got updated info (if you look at that page, you see it was updated in 2017, adding additional millions from the 2009 figures that get most commonly quoted for WW).https://www.the-numbers.com/movie/Wonder-Woman-(2009)#more
While I have no figures and I don't have the interest or inclination to do the digging, I doubt the final numbers TODAY are that low.
What you can argue is that Batman movies will sell well WHEN they are released, that's all. And even that isn't that true because if you adjust for inflation, things like Bad Blood and Gotham by Gaslight are just a bit higher than a 2013 figure for those Superman releases.