Even if Liszt could "play" the first version of the Transcendental Etudes (there are only two versions; the non-existent "first version" that people here are mentioning were selections from a set of exercises, some of which he then based the first version of some of the TE's on), how we define "play" is very important. If one looks at how pianists closer to Liszt's time, like Nyiregyhazi or Cortot, "played" works, then to say that Liszt could "play" those works, in the sense that we now use the word, is possibly inaccurate. However, by that logic, one would certainly say that Alkan was the greatest pianist; I believe that some of his works are notably more difficult than Liszt's most difficult works (version 1 TE's, Grosse Konzert-Phantasie Uber Spanische-Weisen, Illustrations du Prophete). As well, Liszt said that Alkan's technique surpassed his own. But considering the infinitely more difficult works that have cropped up in the past 100 years (Xenakis, Finnissy, Sorabji, Barrett, Hoban, etc.) that Liszt or Alkan never would have even had the chance to "prove themselves" on, it's 100% impossible to speak as to whether they were more technically adept than some pianists who can play works by the aforementioned, post-Romantic composers, because there is no way to compare them. Ian Pace is one such pianist, and once commented that Alkan's Le Preux, "doesn't look too bad," and that Opus Clavicembalisticum, "doesn't present anything that's insurmountable," and he does play quite a bit of Liszt and Alkan. As well, it's important to remember that Liszt was certainly the most famous pianist of his time; Lang Lang is the most famous pianist of ours. Doesn't mean a whole lot when you think about it that way.