I bought 3070s for many reasons.
1) I can get decent mh/s on one rig not have 2 rigs. Used all old stuff I already had with new corsair psu's.
2) Power is highest price in world where I live, almost 1/3 my income goes straight to power (more if there is no sun for solar).
3) If something does happen and mining is not worth it 3070 are sell able, 1660super good luck selling tons of them for decent price. At least in my location.
4) Setup cost was pretty much risers, gpus and 2 psu so roi is quicker. 1660supers would mean need way more setup gear.