Sakamoto cannot be paired with erwin?

I just realized this when im trying to buff sakamoto with erwin but when i buff him the buff is only increase his base damage not the damage after his slim down making erwin buff less effective to buff sakamoto (Taking example sakamoto base damage is 500k when maxed and his slim down damage is at maxed status (max 100% his base damage increase every attack) totalling his damage output 1m/attack... Then you add erwin 100% buff then the damage was supposed to be 2m/attack but it erwin only buff sakamoto base damage making it 1,5m/attack not 2m/attack because i think the slim down only reads sakamoto base damage before getting buffed or erwin buff does not count the slim down passive) should i change erwin with other unit (I don't have any examples because i had no idea) or i just continue to use erwin? Because i had only two damage dealer (sakamoto and honey) the other four is (bulby, erwin, ai (idol), and siren (sometimes i replace siren with speed wagon it's for a quick game to set up sakamoto faster (usually used them in daily challenges)))