Interesting that you think Peter is a better person. There's an argument that a person is what they do rather than what's inside them:
Some of Billy's actions are selfish, fair enough - if charging for autographs offends you, you may wish to avoid conventions.
However, only in the bus incident does Billy put lives at risk, which he then promptly saves.
You glossed over some of Peter's escalating blunders:
1) the guy who he webs to his own car because he doesn't take the time to assess the situation.
2)Screwed up at the atm robbery by messing around rather than just taking down the perps, which led to the destruction of the bodega across the road - and nearly killed the owner.
Props to him for saving the guy, but he caused the problem in the first place and the owner's business is destroyed and he will have a big fight with an insurance company to look forward to.
3) Peter does a ton of property damage to suburban households while chasing Vulture's thugs. Still a hilarious scene but Peter doesn't care that he's wrecking people's stuff in order to chase the van. Maybe there's a greater good argument but it's still not a great look.
4) Peter nearly gets himself killed at the end of that chase when Vulture gets involved - not really his fault but it's painfully clear that he's way over his head and without Iron Man's intervention he'd have drowned.
5) The ferry....where his bungling nearly kills hundreds of people.
So, despite all his good intentions he's incredibly reckless and nearly does more harm than good throughout the movie. It's not his own life he's screwing up but other people's.
I still think that Homecoming is the best Spidey film and the best version of Spider Man to date, but you're making him out to be some sort of saint when he's really driven by a desperate need to prove himself.
Billy is unlikable and selfish at times, but then he was abandoned as a small child and has been bounced around between foster homes - he's much more screwed up than Peter, whose parents are dead but was raised by loving relatives, because Billy knows his parents are still out there - and somewhere down deep knows that they didn't want him. Billy has had a much harder road through life than Peter but still finds his inner hero - so its not hard to cut him some slack.
Billy is the best fit for Shazam's powers because the point of the film is that perfect pure of heart people who never do wrong don't exist - but Billy was the best person for the job, because underneath some of his minor roguery he was brave and compassionate.
And you should try kidding, it worked for Thor in his last two movie appearances. Since he's started kidding he's been much more relatable and his movies have been better.
