How many architects are needed to change a light-bulb?
I would say that it depends on the situation.
Before the light-bulb was invented and we had electricity in our houses, there was a huge need for engineers to get everything in place. So today, we don't need any architects at all to change a light-bulb. Those engineers are needed to make it possible to only use renewable energy instead of oil, coal and uranium.
If you don't do anything new in your organization and only replacing old things with exactly the same, you don't need architects. However. with IT this is seldom the case. This is why we need enterprise architects in our organisatiuons
In my opinion, the number of architects depends on three factors.
The first factor is the scope of the change. If you are making huge changes to your business model and the whole organisation,, then you need more architects in your organization than if you continue with business as usual .
The second factor is the maturity in the organisation in this area. If you need to raise your maturity two steps in order to be able to make huge changes, your need more architects to do this increment than if you are on this level already.
The third factor is more subtle and it is the skill of the architects. You will get more done with skilled architects compared with fresh guys. The challenge is to evaluate how good an architect in the same way it's to evaluate a designer or artist.
Just to give some guidelines based on these three factors and experiences from several years.
If you are on level three in a maturity model and need to make huge changes due to changes in business model (think customers and partners accessing our legacy systems), then you need approximately one architect per 5M € project per / year and you have a mix of experienced architects and more new talent.