It will slow you down because you're forced to confront the consequences of your change in real time, not down the road when someone notices something changed somewhere else that may or may not have broken their invariants in ways they now have to figure out.
Tooling isn't the issue here, you're basically arguing for kicking the can down the road and encouraging a buildup of technical debt.
When you write code, do you put everything into a single function, or do you use separate functions for different parts of the code? Multi-repo is just the extension of that.
Software quality is orthogonal to your development methods. You can have good quality multi-repos or bad ones, and you can have good quality mono-repos, or bad ones.
When I write two functions in the same project I get a compile error if I change the signature of one without changing the call site. This is analogous to a monorepo, in which I have projects in separate directories but with a unified build.
If you really want to take this analogy to its logical conclusion for separate repos, you're gonna have to do something more like compile every function as a dynamically loaded library. And then hope you notice a function signature change because the dynamic linker won't tell you.
Tooling isn't the issue here, you're basically arguing for kicking the can down the road and encouraging a buildup of technical debt.