By making your own lounge inferior to others, you incentivise your pax to go to other lounges (best case scenario), or fly with a non-Oneworld airline (worst case scenario).

Traditionally, when designing a lounge, the airline normally would take into account the profile of their own pax (eg: there is no need for shower rooms in the CX BKK lounge), but the latest trend is to cut costs by allowing others to the lounge. "Others" are not just the pax flying on OW airlines, but also individual contracts with specific airlines (eg: RJ and TG).... indeed some airlines actually subcontract the whole lounge to other airlines for specific flights (when the operator does not have any of its own flights departing at that time of the day).... and you also have airlines allowing Priority Pass and other similar program cardholders... some only let them in during specific hours, when the lounge is otherwise underutilised, some don't have any time restrictions.

....so yeah, I can't agree with you that it's not financially worthwhile.