The damage done to the RR industry by the ICC is an often debated topic. Like many Govt causes, RR regulation may have been necessary to some degree, but the ICC went far overboard and essentially stifled an entire industry till Staggers was passed & the ICC was finally dissolved with the STB replacing it.
Albro Martin makes an excellent case in his book “Enterprise Denied” It’s out of print but can be found at used booksellers. His sequel “Enterprise Triumphant” talks about the RR business post Staggers.
I’d also recommend two other books “Merging Lines” & “Main Lines” which go into the history of RR consolidation Pre & Post Penn Central.
It’s an interesting thought experiment to ask whether if we’d had something like Staggers 10, 20 or even 30 years sooner? What might have survived that’s long gone today?