how do you figure out gaps in team's collaborative patterns? "I will not promote"

Curious how founders actually figure out this when teams grows above 20+ engineers. Like you can hire the best engineers, still they fail to function as teams you expected them to be. let's say something was supposed to be delivered in 2 months timeline but ended up with 5 months, and it's not happening with a single milestone, parts of it are happening across many. doing retro(s) pinpoints that, one was consistently getting slower reviews, decisions were revisited, dependencies were stuck. But how much of it you knew was happening already or the gravity of it, like you were aware of the particular milestone or the thing with the whole team. What systems you adopted as team so these things surface early or doesn't happen at all, and how did you dealt it with each individual, for e.g. one person was blockers to many on a regular period, or someone is too attached to the codebase causing delays. Not looking for just tool names, more from a pov of dealing with humans as system.