I honestly loved that scene from the book lol
Funny enough Shazam's writer also penned the Superman: Man of Tomorrow animated movie. Would seem kind of random for it to be editorial mandate for him to show Jon in issue #1 of Shazam, so I'm actually gonna assume this was his call, and he just really digs the idea of a young Superman.
Speaking of a young Superman, I really enjoyed Jon's voice here to for much the same reasons, but also because the very next thing he says is "now, who thinks I should dump this junk off on the roof of Lexcorp tower?" Straight up super dickery, and I love it! But maybe more importantly, I doubt it would fly for Clark even in his 20s let alone his age now. There seems to be this sense of ease some writers have with Jon's voice. And a large part of that, I think at least, has to do with the fact that this is the first ever in continuity Superman who is 17. You inherently want to write a young adult/teen with more of a youthful flare, and that seems to override that little voice in some writers' heads that sees the S and goes "has to be written stone faced"
I think that's going to be a really big asset for Jon as Superman going forward, and it's honestly something that we likely wouldn't gave gotten with 5G because he'd have been New 52 Clark's age, and even that guy tended to just be written like normal Superman more often than not.
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Also I saw that the issue also to the chance to play up the idea of Jon's attractiveness as a young Superman. I've been saying this from the start, if they can add in a dash of Dick Grayson hotness to the character's whole vibe then that'll take Jon to the moon in a way that Clark can't really swing anymore since he's default dad hot rather than teen heartthrob hot. All this stuff totally adds up, and ultimately helps out.