Pritchard was only eligible for 3yrs/$67M. This the max he could have received for 2yrs. So, while it seems like a discount, he literally couldn't have been paid more per year than he is on this deal.
The mutual option thing is interesting. I just found out with the Podz deal that it means that only one party needs to opt in. So that means that unless both parties opt out, it is guaranteed. Not sure how the doesn't happen unless they work on another extension.
Not sure who pushed for 2yrs instead of 3, but in the end, it seems like a good compromise. Pritchard might have another chance at one more big pay day and the Celtics have Pritchard locked up for 4 more years (including this one).