I didn't before, went off with the assumption that those are the only 2 notable girls he has...
But now we have the complete picture.
I did forget Pluto's combo+ in my argument though, so I'll have to factor that in now...
My breakdown of this goes 2 ways:
You could run Shingen sniper shot with the team, and achieve 45% def break and 40% atk break. The atk break can be capped with Yatagarasu no issue, def break you might want to ignore the last 5%. Pluto with decent lego stacks and Satan combo+ might make it easier for you to catch up with Shingen, but it's RNG. Dice or no dice, I need to sleep after this post so I can't do the maths for you. Still, do consider if you think the RNG is good enough for you to support the burst gen.
2nd option: Hercules PF, which nets you full def break and 20% atk break, hitting 30% with Yata. Everything else about my argument still stands here.
I... will stand with Hercules because in my book, RNG is no dice, plain and simple. I'm not mathing, but I do still anticipate the Hercules set up doing more damage than Shingen. In addition, I don't think you actually need the extra atk break from SS since your set up feels pretty tanky in nature already.
Have a look at other opinions before you make the decision however, them relic weapons don't come in easy to impulse buy.
Going to sleep now, as usual please invalidate me if necessary forum members, I'm digging all this shit straight outta my sleepy ass.