I honestly suspect that the amount of time spent dealing with the issues monorepos cause is net-larger than the gains most get from what a monorepo offers. It's just harder to measure because it tends to degrade slowly, happen to things you didn't realize you were relying on (until you need them), and without clear ways to point fingers at the cause.

Plus it means your engs don't learn how to deal with open source code concerns, e.g. libraries, forking, dependency management. Which gradually screws over the whole ecosystem.

If you're willing to put Google-scale effort into building your tooling, sure. Every problem is solvable. Only Google does that though, everyone else is getting by with a tiny fraction of the resources and doesn't already have a solid foundation to reduce those maintenance costs.

clangd works fine for me with the linux kernel. For best results build the kernel with clang by setting LLVM=1 and KERNEL_LLVM=1 in the build environment and run ./scripts/clang-tools/gen_compile_commands.py after building.