Sounds like you fell for the same pitch I did.
I totatlly understand your dismayed at the results .I hate to see your investment go to waste( both emotionally and financially).
I'm fairly confident you could paint on Bio strip 20 and just the creasing. I know it's not something you can face right now. But it is most definitely achievable, and more cost effective in both time and money.
I know from personal experience it's achievable as I've used this technique to restore a Victorian slate fire place with a period painted marble effect . That was vandalised with spray paint.
If your attending York next month. I'd be happy to take a couple of pieces for you ,and try this technique on them. Then if your happy with the results. It shouldn't take more than a couple of evenings for your to replicate on the rest of them.
It does seem a shame to see all this hard work go down without a fight