Put it this way. My car with only;
Milltek
Revo S2+
S3 Cooler
Evoms Intake
KW V3 Coils
APR Pump
Team Dynamic Wheels and 888's
Did 13.000 on the 1/4 mile
Now assuming you remove the air con core and pump, add lighter battery, lighter brakes with lighter discs, add a bigger intercooler, uprated engine mounts, an uprated clutch, lightened flywheel, wavetrac LSD and loads of other wee mods i dont recall as well as run a smidge more boost, what advantage is there likely to be in a straight line time wise with the "extra grip" you mention?
The thing with an LSD is that its not going to be noticeable until it needs to be active - ie when the car is pushed - and mostly in when the road isn't straight.
Renault and Ford include a diff as they know their customers probably will track the cars. Plus it gives their customers something to discuss in a pub even though they might not have a clue about what it is or what it does.
I won't say I don't notice it on the road but then I probably spend less time on bends than most (think about that

). Driving to work/shops or trying to get an amazing straight line launch on a dry day - you won't see a difference.
PS - the car is a ball hair slower with all that **** added/removed although to be fair, I blame te single mass flywheel for that as 2nd gear is slower to come by with it vs the standard dual
Mass flywheel
Old car with the same wavetrac and standard dual mass flywheel (and less mods) did 12.9 on te 1/4 mile.