I guess I'll say DevOps is hard when done right. I live in a space which has app devs, dev ops, and ops. Since none of that OP's Signs apply maybe we're doing it right. But I would argue it does work well. In reality, Ops is a shared service. Dev isn't. DevOps is a hybrid model and facilitates the challenges of the other two disparities.
As for this off-topic bent on Agile or whatever, be cautious about its evaluation. "Agile" is often just cowboy programmers using that as an excuse for no planning or design at all. And no commitment that has the needed parties in agreement. This is especially painful for shared groups like security and infrastructure.
Agile, waterfall, critical chain, side-by-side, blah, blah are all tools. The best places use those for specific reasons to improve likelihood of successful results. But some kind of planning is required if a business wants to actually create an annual budget and develop projections. Marketing actually needs to know when new products and services will be available MONTHS in advance in order to properly prepare the marketplace. These are facts, not PHB silliness. I suppose if you're a small consulting software shop some of that might not matter, but I suspect most here don't sit in those seats.