Both of you are somewhat correct. There are really two areas where grip is affected concerning any setup change. I refer to them as:
1. Initial grip (initial corner entry or reaction in chicanes)
2. Full roll grip (more mid corner as the chassis rolls to its full lean angle)
Stiffer dampening in the front may give quicker reaction and initial grip when running foam tires on a high bite track. However, it will probably reduce full roll grip mid corner (especially if the track has any bumps). A driver may interpret the feeling as more grip/steering since his car turns in quicker and may not notice any mid corner push unless the traction came down on the track.
Then when you factor in tire slip angles, surface traction/condition and maximum load for each tire, the picture gets even a little more muddled.
There are general rules of thumb that the setup book refers to. However, one small setup change on a foam/carpet car running on a high bite track may give a completely opposite reaction to the same exact change on a rubber/asphalt car running on a low bite track.
Thats why the final recommendation for any driver regarding setup changes is always 'test it on the track yourself and keep notes'.
