Cellulose should be resin impregnated(soaked or sealed) to reduce(actually eliminate) expansion growth... usually an issue with non-resin cellulose fiber caused only by moisture being absorbed, which also decreases filtration flow as the cellulose expands... and was not really an issue ever caused by 'oil'. Synth media fiber doesn't expand in oil either. So, I doubt it was growth unless the cellulose media was sourced back in the 1970's and 1980's. Any time you see resin used with cellulose media, the purpose is to eliminate media swelling which seals up the media. The resin curing allows a more consistent expectation from the media. Cellulose only media is 'variable' micron depending on water content in the oil. How's that for those milky oil caps we've seen over the years?
Take your Bounty quicker picker upper. Works great on water. Soak the dry Bounty in epoxy or supper glue, let it cure/dry, and then try again to clean up a spill, about the only simple comparison I can make for an easier understanding of resin coated/soaked cellulose.
The oil is simply pushing the media around. As long as it doesn't tear/leak, then all is good. The bypass should be low enough to protect the media. Or, the media should be supported, or strong enough, not to be assaulted by the oil.
For comparison, try a synth media filter from Amsoil, RoyalPurple, Purolator, Wix/Napa, Ryco, or the Fram Endurance for comparison with a supported media that has no cellulose.