90 pet packs mean you did Hongsil + RSC on 9 alts every day. That is a minimum of 3 hours/day of doing just events and we gotta do many other dungeons & raids too, so is this a good way to farm?
Further, what do you mean choosing oils over "cheap" pet packs? Oils are much cheaper than pet packs because event currency cost of pet packs is 40% of oils, whereas the market cost is 33% so it is not an ideal option to purchase pet packs over oils.
And going by the past trend not all events are this rewarding, so this way it will take around 6-7 events to farm enough pet packs!