There's not much good to either world. You need fairly extensive tooling to make working with a repo of submodules comfortable at any scale. At large scale, th

There's not much good to either world. You need fairly extensive tooling to make working with a repo of submodules comfortable at any scale. At large scale, that tooling can be simpler than the equivalent monorepo tooling, assuming that your individual repos remain "small" but also appropriately granular (not a given--organizing is hard, especially if you leave it to individual project teams). However, in the process of getting there, a monorepo requires no particular bespoke tooling at small or even medium scale (it's just "a repo"), and the performance intolerability pretty much scales smoothly from there. And those can be treated as technical problems if you don't want to approach social problems. To put it another way, we're comparing asymptotic O(n) with something bigger, neglecting huge constant factors on the former. There's a lot of path-dependence, since restructuring all your repos with new tooling is hard to appreciate.