I'm not sure what that has to do with anything. If UA were to add lounge access to EWR-HNL on the basis of it's deserving of such because "it's the longest flight of a US airline to not offer club/lounge access for F pax," this would mean that whatever is currently the second-longest such flight would then be the longest. Would that justify that flight having lounge access? If so, then the next-longest flight would now be in that situation, and so on. Unless every flight offered F passengers lounge access, there's always going to be one that's the longest without it.

As an aside, the bigger problem is that EWR-HNL and IAH-HNL are sold as domestic F. In the pmCO days, these were sold and operated as BusinessFirst flights, which was CO's predecessor to Polaris. They had full BF seating, catering, lounge access, and all other amenities. The lack of all that is what the problem is - not just lounge access. There was no separate BF lounge back then, but you did get regular lounge access. The shorter HNL flights, such as those from LAX and SFO, were regular domestic F.