Looking at it purely from a descriptive standpoint, I like "Limoss Steel" better for the first option. However, I don't like that the hints use the present tense. On the one hand, this rules out "Perfection," where swords are no longer forged, and on the other hand, it greatly complicates the part of the riddle about "the old being replaced by the new." With the coliseum, on the contrary, the second part seems to fit quite well, but swords were never forged there, and I can hardly imagine how the first part could be used in a figurative sense.
For the second option, reactors also came to mind. But the question is how much they "roar." I like Reimport a little less, because the noise of production wouldn't be so similar, and the noise and power of aircraft engines are still not comparable to reactors, and they, unlike the former, are not so constant.
I didn't have any options for the third one until you mentioned the Grand Duke. For some reason, I was thinking of some martial arts teachers, but in its original meaning, the architect even better suits the title of "grand master." But here the question is really whether all this was in the past.
I have no ideas for the last one except for the Ikigai Gardens.