I don’t think this was a bug rather than just lack of forethought on the part of Jagex, as there’s been a couple forum threads on this and discussion has existed on the forums (without JMod response, granted, but there hasn’t been any mass thread-hiding on the topic as was the case with the Crucible bug) since the Nexus update.
I see this as being similar to the old CVLS degradation moneymaking method, where you bought corrupt VLS’s, degraded them all by hitting one thing with each CVLS, and died with them for money (I don’t think this is profitable anymore). This similarly brought quite a bit of money directly into the game, but wasn’t a glitch. The limiting factor there was the price and buy limit of a CVLS, whereas the limiting factor with the Superior Ports conversion is the time it takes to get the trade goods.
My thoughts are that dying with inventories of corrupt Vesta’s Longswords (and other Revenant/PvP items) to convert them into money isn’t fundamentally different than dying with Superior Ports gear for money, but as always, if you think it’s a bug and a bannable offense, don’t do it.