Instead of banning Heroes from using PvE skills, allow them to take PvE skills as long as them + the player don't exceed 3 in total.
Why? Some classes get shafted in terms of whats available. Physicals can all run SY which makes the party invincible, but casters are much worse off. Monks don't have much worthwhile other than Seed of Life, mesmer PvE skills suck, etc etc. This leads to a massive power disparity between a caster player + 7 heroes and a physical player + 7 heroes. In this case, since the player isn't using many PvE skills they should be able to put 1 or 2 on a hero. This will also let the player themselves run a greater variety of builds, since f.e. physicals won't feel an absolute need to use an SY spamming bar and can delegate this to a hero while they run something else. OTOH, Sins are generally recognized as ridiculously flimsy in PvE (especially heroes that will run right in). How do they become not flimsy? Critical Agility. What won't heroes have? Critical Agility. What does this make Sin heroes? Useless.
TL;DR Not a means to increase power, but let you use more available heroes that would otherwise not be nearly as helpful without PvE skills in exchange for not being able to use PvE skills yourself. It may appear that 3 of x awesome skill would be overpowered, but you have to give up equally valuable other skills you could be running. That's build diversity.
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