Their reason for cutting your access sooner than you expected may have been because they are bitter about you leaving or they are concerned that your new position may be a conflict of interest. They could be concerned that you will be mirroring some of the solutions they have in place (scripts, configurations etc.) and bringing them over to the new company.

I say rather than debate with them over the decision, that you do the best you can do for training the other people without access. If they end up face down in the dirt the minute you walk out the door, that was their decision, not yours.

If they call you after you start your new job charge them a consulting fee lol.