And what, exactly, is limiting usable weapon steel to only a part of the vehicle going to accomplish?
This ‘focused looting’ you’re speaking of requires considerable luck for getting the right books. This, plus the tools, plus the food for all that reading, construction and crafting time requires, at the very least, half-looting a town.
If the player did that, the player has access to over a dozen cars to loot. If the player can loot that many cars, the player can obtain as much quality steel as they could possibly want, regardless of whether only some of the vehicle is usable or not.
On top of all that, while serviceable at endgame, they aren’t even endgame weapons. They aren’t on fire, they aren’t diamondized, heck, the player doesn’t even have the skill to use them effectively if they monofocused like that, and they definitely don’t have the mutations and CBMs to truly make those weapons shine rather than being ‘pretty decent’.
You’re talking as if the player would be barely a few steps from being as good as they can get, but the reality is that they are still very far from being more than adequate.
Another way of looking at it is that if they put half the effort and luck in archery, they’d already have high skill in archery, one of the best bows and the best non-explosive arrows.
Put the same effort into a vehicle and they’d have a working and semi-reinforced one even under bad luck, possibly with a couple amenities.
Put half the same effort into cooking and you’d be making high explosives, and be a few steps from making mutagens.
All of these would allow dealing with hordes in direct combat. The PC that went for the melee weapon, on the other hand, cannot do this yet. They don’t have the skill to pull it off, nor do they have the armor.