I don’t ever recall having issues getting a broad range of serviceable resonant tones from the Mark 1 with its variable filter (Filter 2) (Filter 1, the ladder has a very narrow usable tracking range by comparison)
Fwiw - I can play 6 octaves of very usable tracked filter resonance on the Mk2 and that was my recollection on the Mk 1 as well - you get at best a jazzy 3 or 4 from the ladder by comparison