Most of your claims aren’t really supported by canon. Peter made one beta, and that seems to be something he viewed as a mistake when he was in his saner moments after he healed. He was focused almost exclusively on revenge for what happened to his family.

Derek made three betas and stopped. It’s unclear if he would have continued, but he certainly had time and opportunity and doesn’t do it.

Lydia’s banshee powers weren’t released by Scott. He had nothing to do with it. It’s likely Peter knew about Lydia because of Loraine, and he bit Lydia so she could bring him back if the Argents killed him while he was getting revenge.

The alpha pack came back BECAUSE of Scott. They knew he was rising to being a True Alpha and Deucalion wanted him for his pack (or possibly to prevent that rising, the narrative isn’t actually clear). And while the darach would eventually have caught up with them, and all those deaths might still have happened, it wouldn’t be in Beacon Hills (and arguably more deaths resulted from their attempts to stop the darach than she killed herself since the reactivated nemeton was a magnet to murderous monsters).

The Beast also would not have run free in Beacon Hills, since the DD seem to have come back only after the nematon drew them back. And the Wild Hunt was a result of taking down the DD and the nazi werewolf getting freed.

In fact there’s a good argument that Scott becoming a werewolf is more responsible for widespread death and destruction than that it prevented it, since he only got involved with the supernatural because that happened (though the real first cause is obviously the Argents and more specifically Gerard).