you're right about the physics, the car will always be perfectly balanced.
but with less grip it's defiantly harder to drive especially on full tanks
and the player no longer has the grip advantage over the Ai so overtaking
is a lot harder.
without the patch the player always has 16384 grip whatever team driven,
hence why you're putting a minardi in the middle of the grid, once the tracks
are calibrated to your own skill level then you should be sitting at the back of
the grid when driving a minardi.
you won't get oversteer but you do get understeer due to the lower grip level.
if you drive a ferrari and then a minardi the difference in grip is very apparent,
for example turn 5 at melbourne is flat in the ferrari, but with the minardi you
should find you have to lift and that's with 90bhp less (2001 season default track
setups), in real life a poor chassis will produce less grip, so it's half way there.
the teams performance files were originally for gp4edit, but as rene's now updated
gpxpatch, these can be used in gpxset, car power team dependant needs to be ticked.
the excel sheet is just used for competing as a career and works out grip levels
exactly the same way as I calculate Ai grip levels for the season performance files.
http://www.belini.fsnet.co.uk