That's the main issue for me.
It's kind of like proclaiming the Ford RS200 was a "racing prototype" and then discovering that it doesn't do anything better than Vauxhall Astra or VW Golf of the same era.
The Mamba probably should have compromises if we consider it's origins HOWEVER, in practical terms, if it's intended to be a viable alternative for the FdL it needs to be able to compete with the FdL on even terms.
That's not to say it should have the same strengths and weaknesses as the FdL but it should have it's own features which present the player with a viable choice.
Right now, the only reason to fly a Mamba is if you don't actually like the FdL and you're prepared to accept a ship that's objectively worse instead.
And that's not a good reason to choose a ship.
Which makes the effort taken to design and implement it a waste of time.
Sticking with the theme of being a "racing ship", the Mamba should almost DEFINITELY be lighter than the FdL.
Maybe racing in the 34th century also involves inter-system travel, in which case maybe the Mamba should have a larger FSD than the FdL too?
Also following the racing theme, maybe it should use less juice to boost, like the Krait does as well?
In a nutshell, right now the Mamba is a bigger target than the FdL with nothing to compensate the player for that disadvantage.
It needs some advantage of it's own.