A -1 or -2 damage roll malus is hardly going to make a difference when you're using your ranged weapon as filler, and handing that guy any non-crafted magic bow would make it even more irrelevant. The arbalest is a god awful weapon to use as filler (or in general) because of the full round reload. You will never fire that thing more than once per encounter unless you go out of your way to do so or take rapid reload. Regardless, the point was never whether a caster should spend a feat on crossbows or bows. Both options are obviously unappealing unless you plan to switch the feat before leveling or get the group proficiency for free to begin with. The point is that crossbows have no real niche or purpose. Why even place action economy-centric restrictions on them as though you need to contain the earth shattering might of 1d8, 1d10, and 2d8 with -1 to attack rolls? They're all around terrible and "just something for wizards to do for their first few levels" doesn't justify three weapon types and an exclusive feat. Hell, even slings have a niche of being able to apply bludgeoning enchants to a ranged weapon. Being able to instakill a ghost dragon by chucking ghost touched undead bane+destruction rocks at it is kosher, but simply wanting xbows to be viable in any way beyond being a slipshot wizard cantrip stand-in is silly?
I'm not sure about the point of your argument.
Some weapons sucks, light maces for example, just don't use them.
One thing I disagree with though, 1/2 damage can make a huge difference, often, mostly in the village, some enemies will survive with 1 or 2 hp and it will allow them to act again, which could lead to a disastrous outcome.
Then again, if you absolutely want to use a crossbow but can't affort to spend one or two feats necessary and it makes you horribly mad, just change the feat settings once or twice for that char level up and then use crossbows.
What stopping you?
He's a mage but he spent some time hunting with a crossbow as a kid. He's not a sharpshooter but he's gifted, hence the 1/2 bonus feats.
It's as simple as that, you don't even need the justification as there's no GM to validate your choices.
Problem solved.