The higher weight of Helix comes from its frame and heavy helicoidal folding system. The ultralight Helix already uses lightweight components and it won't be possible to lower its weight while the 7.95kg of the T-line includes components like mudguards and lights not present on the Helix that should be removed to make a fair weight comparison.

The frame of the T-line weight less than the Helix frame and smaller wheels with equivalent components weight also less.

Moreover, components of the T-line like the brakes are the same as on the other Brompton and aren't lightweight, so it will be easy to reduce the weight of the T-line.

If performances is the goal there are much more efficient folding bikes than the T-line.

And wheel size is not the dominant parameter that define a bike efficiency, other parameters like tires construction, width, pressure, frame efficiency, position on the bike... have much more influence on efficiency than a 40% wheel size difference (compared to the T-line 35x349 wheels) or 28% difference (compared to a Birdy with 50x355 wheels) or 20% difference (compared to 40x406 wheels of a fast folding bike like a Tyrell or a Pocket Rocket). The problem of Helix is that there are no high performances tires in ETRTO 40x507 or less that fit on the Helix.

BTW, the Helix has no real 24" wheels, real 24" wheels are ETRTO 51x507 wheels while Helix cannot accept tires above 40mm, its a 38x507 folding bike so something like a 23" folding bike.