Not sure where your JP friend got their information, I've been on JP and know there's a slicer equivalent coming for a scion class when released. It might not be named slicer though and function even more differently than the PSU slicer did which might be where the confusion came from.
I would accept this if they gave us literally ANY slicer from a previous game in the form of a talis to reinforce this; I was actually looking forward to that when hero was first shown off, but they just haven't given us anything as far as I can tell
for the record; I think the only other weapon types that haven't gotten a representative in pso2 are like, PSU-exclusive shotguns (spread needle was a shotgun in PSU, but none of PSU's original shotgun designs have made it over into pso2 (slug shotguns would make for a passable rifle imo)), and PSNova's Piles and Halos, but those are kinda probably in their own limbo due to technically being in PSNova I guess.
I suppose this could technically mean they might had initially been saving Slicers and Shotguns for something but I doubt we'll hear anything about it now