I think, we should see the "Four (4) groups of People" as "temporary qualification in time".

1) some people are "ready"

2) some people are quite ready but can be ready in a short time

3) some people are 'not ready' but with training can become 'ready'

4) some people are 'not ready' and are not interested.

We all are in different groups for different matters at different times.

--We are not "born" to be in one group.

But we are growing through groups.--

We can choose to be in whatever group by practice "proper Buddhism daily".