Only works if you have multiple teams with similar specializations. Often even in quite reasonably sized companies you have many teams that are the only ones do

Only works if you have multiple teams with similar specializations. Often even in quite reasonably sized companies you have many teams that are the only ones doing that thing in the organization and you need a team lead who knows the exact thing the team is doing, so you either promote from within the team or hire from outside (which has its own problem of communicating to the team that they have no possibilities for advancement unless they go to work for a competitor).