That's a good point, and one lost on the many folks who casually practice Czerny's exercises, but never bring them up to the proper, i.e. Czerny's, tempo.

It's a long way musically between Czerny and Alkan -I hope no debate there- but in Lewenthal's preface to his edition of Alkan, he makes a point which could equally apply to Czerny:

Read his markings scrupulously, starting with the metronome indications, which at first will usually seem too fast. They are not. It is you who are too slow! After you have acquired thorough familiarity with Alkan's music, the metronome indications will seem perfectly chosen.