The point is good, or at least better, game design. Convenience is supposed to scale with progress, that's the definition of progression. That way it's more rewarding when you get it.i feel like since the amount of players this change would affect is so miniscule, and all it does is remove convenience for those players, i don't think it's worth doing.
i feel like it's safe to say that the majority of players who get significant usage out of the grand design either do a bunch of funky fun stuff with wiring, or they use it to set up teleporters in hardmode, post-mechs. the latter group, which i can only assume is larger, is unaffected. meanwhile the first group is just inconvenienced and annoyed.
besides, the individual wrenches are still useful when you're tight on cash. i know it's not common for a lot of players to be unable to afford just a bit over 12 gold, but it happens. especially on classic mode, where money isn't rolling in as much. i just don't see a good point to this.
That said, you're right that wiring only really comes into its own for most people once you get the Steampunker, which I suppose is the bigger issue. Most people only find themselves actually wanting to do wiring stuff once they get her and by then it's super easy to just buy everything you need for the Grand Design. No real way to fix that and even if you could, it'd probably take more effort than it's worth for something so minor. I guess it's fine the way it is.
I do still want something to be done with the Ruler, though, since it feels out of place among the Grand Design's ingredients. Either replacing it in the recipe, or giving it an extra functionality that at least has something to do with the Grand Design. Giving it the ability to draw a block ruler anywhere on the screen would work perfectly since it mimics the Grand Design's ability to draw wires anywhere on the screen, which is also the Grand Design's only functionality that it currently doesn't inherit from any of its ingredients. May not be possible at this point though.