You don't slot in anywhere as there is no 'list'. You join in the role you are offered and probably applied for (SO, FO, CPT etc). I'm sure you must have some awareness of how these things work in other non-seniority operators so I'm not going to waste time explaining.
Whether its fair or not is debatable (as is the idea of time in the company being the sole determinator of everything) - I'd lean towards the idea its fairer. Transparency is a real issue, however.