When I think about S3, I can't stop being frustrated about how much better they could have written Billy's development and overall situation.
They could even have used the exact same intro scene for him if they needed the unnecessary Karen moment so badly in season 3.
Imagine Billy walks in, starting his shift, everything happens the same with the flirting and all, but then Karen wakes up by the pool, has another of her Billy is the spitting image of the book cover boy novels resting on her chest, looks over and sees Billy giving swim lessons to children, including Holly. She gets over it quick, maybe by looking at the book, realizing what it does to her mind and throws it in the trash.
Billy is great with the kids. They love him and he is happy, hearing them laugh and giving their best. He will buy them ice cream after each lesson.
Billy is getting better with Max, too. They still have a bit of work ahead but he's trying.
After work, Billy will go to Scoops Ahoy just to laugh at Steve in his beautiful, new sailor outfit. We will assume he's bullying him again but then it is revealed, they became friends and he is picking him up to see a movie and after, they both drive home separately and Billy has the accident.
(They can have the same Scoops scene introducing Robin with Dustin coming back and Robin can ask Steve if he's only friends with children but then Billy shows up and she could say sth like never mind, I prefer the children)
The mind flayer got him. He comes to work not being himself anymore. The children notice. He is dangerous for the children, has a vision of killing them but the real Billy is stronger and he sends the kids to safety. Maybe Karen confronts him to ask what was going on because he scared Holly and he has a vision of killing her too, telling her to stay away. Still same things happening but better, imo.
In this version, Max really starts to worry about Billy without a 'part of her wants him dead' twisted mind. Why is he so weird? They were just starting to get along and she felt like having a real brother. They will try to save him because they care and it will hurt even more because they can't. (I would prefer him surviving and joining the gang of course but based on Dacre wanting only two seasons, I go with his death here, too, just thinking of it being more impactful.)
No one really cared if Billy would burn with the car or that the fireworks hitting the meat puppet hurt him in the actual show, so having him and Steve actually be friends would add even more emotional impact to that scene with him having to watch how every hit hurt Billy and El could still try to get to him through his mind, passing his deepest trauma until she finds the recent good memories, the kids laughing and splashing water at him, banter with Steve that ends in them cracking up laughing, him and Max having a good moment... and then he gets up and turns around to give his life to save his friends and family.
RIP Billy Hargrove, you deserved better.
(I was just rewatching a show where my favorite character started as a villain type, absolute horrible character but had one of the best growth and development with a tragic ending that hurt but also didn't feel wasted. I really wish Billy had something like that... His character just feels wasted in s3...)
(Also please don't use this to hate on any character)