The issue with Mercurial Scimitar

Is not the 75 AD.

Reducing the damage by 10 is not going to fix the base issue with this item being too good with no real down side making it situational.

The issue is that combined with warlords bloodlust it can easily become a no real trade-off item for getting in place of Bloodthirster.

Make it cost 3400 and have 75 AD, 35 MR and the active but get rid of the life steal so there is a trade off for getting this item. And since this would change it up a bit make it build out of QSS and BF Sword again.