A few clarifications to be made here.
The primary aim of the team, as Grummz has reiterated, remains to re-capture the mobility and feel of Firefall. That has not changed, atleast there has not been any explicit statement from Grummz saying 'This is it, we are going with this'.
The majority of the original team that built the mechanics in Firefall, are not associated with Em-8ER. Thus Grummz and the current team have had to start from scratch to build these again, with little by way of 'reference' material. The only reference they have are old videos, and those do not provide enough data to rebuild mechanics.
Back when the team was setting off working on the jumpjet systems, Grummz spent a lot of time talking on discord, collecting feedback from the community on how the jumpjets worked, how they felt, whatever folks could remember. Everything currently available in the demos are a result of what the team has managed to put together based on that feedback, input from reference material and their own experience/memory.
It follows, then, that what they develop initially will never feel as smooth as Firefall did. The jumpjets themselves have had a bit of rework done to them over the last few demos. Momentum, inertia, weight, have all been adjusted to allow for better handling of the MEKs.
The game is far too early in dev for anything to be set in stone. Mechanics and systems will have a lot of change over time, to the point they become unrecognizable from what we have today. It's just the nature of game dev. And that is the purpose of these demos, so folks can try out and suggest improvement/provide feedback on how to recapture that old Firefall feel.
TL;DR: Game is very early in dev. Nothing is set in stone/finalized. Changes and improvements will be made to mechanics, based on community/tester feedback. So fire away, the team is definitely listening.