Been there done that.

Moulton TSR souped up is still a heavy bike that even though I can ride with road bikes, its not going to accelerate as well if the pack surges (especially on climbs and downslopes ).
The suspension is a double edged sword and robs power (yes, in theory we can talk about 'smooth' pedaling, but when the hammer drops in a group ride, there is less luxury to ease into the power )
It does ride like a luxury car though with a stately planted and smooth feel. (this is what I really miss and can't get back on any other bike I have used )

The Brompton though, is still far behind for fast riding, even vs the Moulton.
Draggy IGH, lack of right gearing when the legs are at the lactic threshold (and other riders surge some more ), small wheel = more rotational losses and prone to road imperfections )
It is perhaps the best bike that folds into a small package.

So in the end, right tool for the right job.
If I travel, only do short rides, then the Brompton is better.
The case of the Moulton is much weaker nowadays, there are better folding bike options that fold faster/ easier, give comparable rollover on poorer roads, less heavy, less maintenance. (Change Bike; Montague; Birdy; Various Dahon like folders with plusher tires )
Its a nice bike though, just that its use case is less travel and more of a ride it with the occasional travel.