I agree with the covering of several roles, I disagree that this is an issue.
I think the issue, is that they cover the exact same role, just orca is worse at it : they should cover a very different way of doing that role.
what I propose : keep the same yield for drones ; but increase their cycles to like 5 minutes, or 10 dunno. so they have 5-10 times the hold,and if they are mining the same rock, or if they are out mined by a barge, they will lose on the volume.
This would be true for mining drones, ice drones, excavators, and ice excavators.
This would also be a neglectible increase to effective yield, since the drones would need to move less, per unit mined.
The idea is that they become specialized in mining big rocks, not small ones. Fitting a survey scanner on orcas would also become interesting to not waste 9 min mining a roid that had 1min of yield only,
IMO the cycle time should be :
excavators 20min ( = 4 indus core cycles)
orca 5 min
barges 1 min
from venture base, the cycles are *1, *6, *30, *120 in terms of cycle duration, giving each ship a role : venture is better at cleaning the small dust, rorqual/orca are better at eating enormous/big rocks, barges and exhumers are better at eating medium rocks.
This also means that people who take the time to visually identify the rocks size, can optimize their mining without having a survey scanner.