Still it needs to enter the cells all the same.
As for being localized it's true however after vaccine dose S proteins have been detected also in remote locations in the body because you can't make something 100% localized.
If you had an infusion that doesn't trigger immune system you could just increase the dose significantly, put it in the blood and most likely it would have reached all cells that blood reaches.
Last I heard those gene editing things lead to so called of-target edits, so they were basically corrupting random dna. Now in this case the baby would have died without this treatment so clearly benefits outweight the risks. But even then they probably want to have the dose be as low as possible.
But I'm speculating a bit here.