I think your examples do not really prove the role of visual design conclusively because in the 18 month time-frame, the folks at Groove must have had several efforts running concurrently with the explicit goal of increasing revenue. The web site facelift you were engaged for happened to be one of the steps they took towards that goal.

For instance, they would have intensified sales, marketing, customer success, fixed bugs in the product etc in addition to the revamped website, so we can't really pin the significant jump in revenue from $1m to $5m on visual refresh alone.

Not trying to diminsh the work that you did, merely trying to put things in perspective because our tendencies as humans is to misattribute causation, which is bound to happen if all contributing factors to a thing's success are not properly considered.