It's not like the spirit of the questions changes... but, whatever. I guess I'll be sinking with my ship in solitude; pity.
There's no reason Rin would have to forge weapons herself, there are blacksmiths for that. Do you really think Minato personally crafted each of the kunai he applied the Hiraishin seal to, when he could just order them made to his specifications?
Also, the legendary blades of the Seven Swordsmen can't require exotic maintenance since their wielders know nothing about methods the Uchiha used in their creation. If even those masterworks don't need it, I doubt Rin would have to worry about loosing all that much time to maintenance.
Rin is a perfectionist who remembers just what quality weapons can be at their best. I doubt there's a smith in the Land of Fire she'd be happy with, not to mention that alchemy opens up options that are outright impossible to local smiths. Yeah, outsourcing is an option she'll take if necessary; but not for her own weapons, that much I am confident of.
Easily? Futhark runes are something many magi study for their entire lives without ever getting to that level.
Bazett's use of runic sorcery for enhancement was a large part of what made her an elite enforcer. As for Touko, according to her wiki article Ansuz is one of only three 'primeval runes' that she ever learned to replicate, despite being "one of the most powerful magi in the world".
Also, you seem to forget that we only sacrifice "directly offensive Elemental Magecraft" - indirect methods are still possible, so the field of attack vectors we loose and can't replicate with jutsu is incredibly narrow.
Quite easily, yes. First of all, and I can't emphasize this point enough, the Ansuz used in Kara no Kyoukai part 4 is modern rune-based magecraft. It is
not one of Touko's three primeval rune replicas, which could amplify any other runic curse she used a million fold and which Aoko had destroyed years before the events of KnK. It is also mentioned that Touko's runes became weaker in general after that. Furthermore, replicating any primeval rune at all is a most impressive accomplishment. They are mysteries from the Age of Gods that shouldn't even exist in the hands of a modern magus; Touko's possession of 3 is a massive flex and a notable part of what validates her status as "one of the most powerful magi in the world". ...But I digress. Yes, Touko is exceptional; however, her runes after the loss of the 3 replicas are still normal runes.
Secondly, Bazett should never be used as an example of modern rune-based magecraft, or... anything related to modern magecraft, really. Her mysteries are potent but exclusive, preserved from the Age of Gods in the Fraga bloodline. They are powerful but not developed in the sense that modern magecraft is by necessity.
Now, moving on to the crux of the matter... Runes are one of the most stable, oldest, and easily available foundations in modern magecraft. Simply put, this means that there is a lot to study; versatility and adaptability come at a price (of putting in even more effort than other, more specialized foundations require). Tohsaka's explicitly specialize in
energy transfer. Rin, even young and inexperienced, can reinforce objects, and even her body, selectively and precisely on the fly. Learning to fry people's hearts is not a great leap from there, if not exactly in character.
(...Random thought: we should be able to easily develop a magecraft-based version of basic Jūken, unless chakra flow works to counter magical energy similar to how magi can prevent any direct interference with their body via prana cycling. It'll be like returning to the family's roots - prior to meeting Zelretch, Tohsakas had specialized in esoteric martial arts, after all.)
On account of "only losing directly offensive Elemental Magecraft": with directly offensive elemental magecraft being limited to jewels, all other potential vectors of delivery are cut off, thus limiting combat use to basically single use bombs of lower yield than chakra techniques for the foreseeable future. There hasn't been much magecraft researching in this quest as is; I don't want to discourage it even more. Also, I think you greatly underestimate the amount of versatility we lose with that as well as the amount of versatility magecraft can allow for.
