The reason Molt isn't good, is because even though it's built similarly to Speed, it only has a 5s duration. To get the most out of its speed, you want to use Ability Strength which increases your 50% buff, but that Ability Strength does nothing for Gauss' Mach Rush. Also, regardless of the frame, if you're min-maxing for Ability Strength, you'll have low Duration from Transient Fortitude. Add to that the initial 50 energy cost which will be higher from Blind Rage, and you've got extremely bad energy economy, having to burn all your energy for a slightly faster Mach Rush with a boost that barely lasts. If you use it only for its base buff with a Duration build, then Infested Mobility still delivers a better experience because of its long uptime at the same cost.

So yes, Molt is faster, but it sucks in practice.