OK, here goes:
If you are shooting a film at its true speed and it is a low contrast film, shooting a modern modern lens will give a bit more contrast if you desire it.
The higher the speed of a film the lower the contrast, as long as it is rated at its true speed.
The true speed of Delta 3200 is about 1000-1200, Neopan 1600 about 500-640 etc for ME with my devs and technique.
If you are pushing a film beyond the true speed in your dev combo, this will result in lost shadows and stretched highlights i.e. high contrast negs
Modern lenses reduce effective film speed because they are low on flare. Older lenses with less effective coatings are higher on flare i.e. light bouncing about inside the lens and spilling into the shady areas and helping to increase exposure in the shadows. Modern lenses will therefore produce therefore darker shadows for the same given exposure. If you expose more to open up those shadows with a modern lens, you get hotter highlights.
Therefore:
Shooting a modern lens on a low contrast film in a low contrast situation would help you out by maximising the contrast on the neg and preventing flat contrast on the neg.
Shooting a modern high contrast lens with high contrast film or on high contrast situations may lead to high contrast negs that are hard to print
Shooting an old lens when you are pushing film beyond its true speed or in high contrast settings will assist in opening shadows and controlling highlights.
However:
None of this really matters. Get used to your lenses, films, developers etc and adjust film speed and development to get the neg contrast you need.