One Hierarchy, one set of schooling, one set of ranks. "Everybody is an officer" and goes to the same school for the same things. No divide.
On the contrary, your proposed "no divide" is fundamently and intrinistically far more elitist and divisive than the streamlined "single track, two entry points" system that Starfleet has been shown as having
no later than mid-
TNG.
Because if you insist that "everyone is a
commissioned officer" ie an Ensign or above, then only those who have schooling, connections, intelligence and mindset to spend four years on degree level schooling are
allowed to be part of Starfleet, everyone else is excluded because they "aren't good enough".
On the other hand, Starfleet -- recognising that practical, non-academic types can be useful if you play to their strengths -- allows said people to initially take shorter, more focused courses that lead to a specific role, then implicitly gives them the opportunity
if they wish to expand on their qualifications and get promotion to the managerial officer ranks in time. In fact, dialogue from
Flashback seems to suggest that a motivated "Specialist" can actually gain promotion all the way to Ensign
quicker via that route than the Academy (We don't know
when Janice went for officer training, but she specifically tells Tuvok that she completed it in
three years, rather than the
four or more that new entry candidates spend there)