The short version is:
If you dont jump nor race or ride extremely powered in light wind, it does not make sense to buy new lines for a bar with same thickness/strength as for your TT/Waveboard bars, would be stupid as I see it.
Line lengths are different anyways (in marginal winds) meaning not the same bars used.
So best guess on how much lower in strength will give the best "match" for similar overhead, is the simple question ?
If our normal frontlines are 270 kg, and rearlines often the same for simplicity, so 270 / 270 kg, my best guess for lightwind hydrofoil linesets would be:
170 kg is sufficient, and for the rears 100 kg lines could be used, still having some margin.
Just my guess, but interesting to hear others experiences and knowledge
PF