As you probably know, the Ring of the Marksman, the Harley pet and the Acina's Tricorn give some bonus to some weapon's effects, like the AoE of Citzal's Spirit Lance, WotEP, Amra, Keeper of the Flame etc. and also weapon's abilities like Thunderous Report and others.
The Sharpshooter subclass give also +1pen and 15% crit chance with these effects, like other Passives from the ranger side (like Marksman).
I made some test, so the fire damages from Keeper of the flame on myself have the +1pen from the subclass (<4m), but not from Marksman talent (>4m). In other side, Thunderous Report on far than 4m targets have +5acc from the talent, but not the pen bonus. That mean, for melee AoE weapons, the subclass is advantageous, anf for other effects (>4m), the class is beneficial.
I thought that can be interesting to know.