Alkan's biggest technical difficulty is that his music is incredibly transparent, and often relentless, even in the most difficult sections. One can't just use extra pedal or extra rubato without most likely sacrificing the overall musical idea. Liszt's music is much more chromatic and "romantic" if you will, and while I wouldn't immediately say his music is easier than Alkan's, it's not always as relentless or transparent in the same way.
If you make one mistake in Alkan's music, it's incredibly obvious, just like Bach, Haydn, and Mozart.
As far as your specific comparisons, it's kind of tough to say, as it will differ between pianists. But in my opinion, as much as I love Alkan, Le Preux just isn't a good piece. Alkan was hit or miss, and while he hit more often than he missed, Le Preux is a miss...