Absolutely! At some point you must invest in your tools. (Early, in my opinion.) I think the clarification I’d offer is that in the age of GitHub the “standard” model is multiple repos, so you’re actually giving up some tooling if you just shove everything in a single repo.
(I’m also not sure I’d generally categorize tools work as as “dev ops,” though I can certainly see how they end up intertwined.)
I've seen hardly any tools to manage dependencies across multiple repos. Modifying multiple repos at the same time isn't an issue I see many resources devoted to, and managing those cross repo versions is almost never done well. In comparison, both buck and bazel offer pretty mature monorepo management tooling. On the VCS front, you can take native git/HG a long way.
(I’m also not sure I’d generally categorize tools work as as “dev ops,” though I can certainly see how they end up intertwined.)