Furthermore,
> they're held together with a fragile weave of scripts, hacks, unsupported hardware and outdated knowledge
Swapping out COBOL for typescript and mainframes for linux boxes and a pile of YAML is not going to change any of that. People can and will build garbage with any set of tools you give them. Not ever software problem is like use-after-free where you can fix it forever with a sufficiently clever piece of tech.
It can be, depending on the system and who's complaining about it. Sometimes a fragile, buggy, mess of a legacy system is actually fragile and buggy, with failures causing downtime or lost business, and creaky processes slowing new development to a crawl. Sometimes it's just a system that has an unfamiliar or slightly less ergonomic developer experience, that uses older technologies that some developers don't want to learn. You have to look past the complaints and judge for yourself.
e.g. https://www.computerweekly.com/news/252446965/Lidl-dumps-500...