For purposes of my answer / opinion, there are two categories to place a ML into...Traditional, or Modern High Performance.
In my opinion, the whole distinction or design point of a "traditional Muzzleloader" has its roots in the "early American traditional muzzleloading era".
One school of thought ends that era around 1820-30 when caplocks were invented, limiting "traditional" to Flintlocks.
Another school of thought ends the era in the Civil War when cartridge guns were invented, and so includes Caplocks.
IMO, I include both Flintlocks and Caplocks as "traditional", but with the Flintlocks clearly being the primary firearm for many decades in our country...and caplocks appearing after 1830 and for a shorter period of time as cartridge guns began appearing soon after.
Therefore:
A traditional muzzleloader is both a Flint and Cap side lock ML, with exposed flint and cap ignition systems, open "iron" sights, designed & styled with a look and feel that anyone from the early American traditional muzzleloading era would immediately recognize as being representative of those rifles commonly used back during that era...and that means no scopes.
A traditionally oriented design of a ML may be a hand crafted expensive custom-built precise replica of a specific model rifle from "back in the day", or it may be a mass produced muzzleloader with a more general traditional design, like a TC, CVA, Lyman, etc. The custom built precise replica may be more period correct than the other but both are clearly in the category of "traditional design" from that early American traditional muzzleloading era...and that means wood and metal as opposed to plastic.
A traditional projectile from that era would primarily be the lead round ball, with the late period inclusion of a lead bore size conical...and that means no plastic, no sabots, no copper jacked bullets, no plastic skirt bullets, no alternative metal bullets, no modern bullets, etc...if a projectile was not commonly used in MLs back during that era, it would not be considered traditional.
The traditional propellant is real black powder which was the traditional propellant used in traditional muzzleloaders back during that era...and that does not include modern made 'BP substitute' powders or "smokeless" powder.
Our whole country was founded with the traditional muzzleloader as the common firearms technology available at that time, and the whole point of someone acquiring, learning, and mastering the use of more primitive "traditional" muzzleloaders is to accept that challenge and keep that part of our history alive.
