Situations like this are never ideal, and no apologies or excueses will make the situation right. Based on the OP's description, it looks like there are opportunities where UA could have handled the situation better, and it's definitely unfortunate that a new plane wasn't ready sooner, or a new crew available to take the second plane.

No one wins in situations like this and the OP has every right to expect a better experience in the future.

My apologies things didn't go better.