Ok you can't take what they did in halo ledgends seriously its an Anime made by japanese people that is why all the buildings look japanese. Nothing but artistic license. About what the ODST said [quote]"The architecture is not Covenant design and it sure as hell wasn't built by humans. It pre-dates both sides."[/quote] The ODST and humanity as a whole did not know much about the forunners because ONI kept it locked down. But as you said Spark says "you are forunner" he is crazy but the only humans are able to activate forunner tech. MC is called a relcaimer because he is reclaiming what the forunners had lost to the flood. You ask why would forunners build all these instilations if they were losing a war. I ask how the forunners would change all there tech to acommidate humans and not anyone else. Forunners could create entire planets and suns they had the tech to create the crystal in first strike also. Precursers were teir 0 they either left the galaxy are trancended time and space. The forunners recived their religion "the mantle" from the precursers before the precursers dissapeared. The forunners wouldn't allow the precursers to de-evolve after recieving the mantle.