It's not true. All the nonsense above about Al tubes having thinner walls are BS. Even with oversized tubes, the aluminum is two or three times thicker than a light steel tube, as well as having double the diameter. Super lightweight steel (when it was common) was much easier to dent with its 0.3 or 0.4mm thick walls than modern oversized aluminum is with 0.9 or 1.1 mm thick walls. Conventional wisdom has always been that steel bikes could be made much lighter by making even thinner tube walls, but they would be too easy to dent even though the frames could theoretically be strong enough for regular riding.

My understanding of Reynolds 853 is that the alloy was originally used for car body panels because of its dent resistance compared to other steels, so modern lightweight steel frames are likely better than the fragile and dentable steel frames of yore, and likely as dent-resistant as aluminum.
Source: Lightweight steel racing bikes in the past were much more commonly dented than aluminum lightweight bikes are today.