Assuming you used T&G flooring grade chipboard (ideally P5 bathroom type) I'm struggling to understand why it's unsuitable. The T&G flooring chipboard I have in my Bungalow in the UK has been down for 28 years and still as solid as a rock. The T&G chipboard flooring put on the joists in my Lounge in France by the previous owner is also as solid as a rock, although I was going to cover it in either Lamininate or wood veneer flooring to make it look better.
Yes, flooring grade chipboard looks cheap, it is unattractive, but it works. A coat or two of PVA wouldn't go amiss but obviously any paint or covering which didn't have any wear resisting properties would quickly fail depending on traffic, but then you would expect that. Perhaps something like 'Deck Paint' would work ?, I've used it on Fibreglas and Marineply and it wears and stays on well.