One complaint I've seen is that the ATC should not have let the helicopter do visual spacing in that regime, that it was somewhat careless and unsafe and possibly discouraged. If the ATC operator was overloaded with work, they would be incentivized to "outsource" the spacing management to the helicopter who would then be able to screw it up by "seeing" the wrong plane. I can see the merits of the argument but it would take the NTSB to have the right knowledge to confirm or deny it.