Sir your fabric of connectivity has fallen WAY behind the tech of the trains that are running on them. When trains capable of higher speeds are forced to slow down because your tracks cannot support them, it's time to IMPROVE.
Entire world is using track relaying machines for more than 5 decades. Track relaying is different from laying entire new tracks. The SVM-1000 which is used to lay new tracks where no tracks existed before is quite modern machine. The is sourced from plasser and theurer. Other older machines required existing tracks to renew those tracks. China using such machines in 60s and 70s is exaggeration. Even germany didn't had machine like SVM 1000 in early 2000s.