An Interesting Thought...

[wolle1301]

In Iconography the depictions of Retiarii are neither better nor worse than those of other Armatura depicted without helmets.

Maybe, but in texts you always read about retiarii as the "beauties" in the arena. And I strongly believe, if you put up a show, where most of the participants wear masks, you will never ever appoint an ugly one to not wear one.

Also your Chart does not take account of other common Armaturae, like the Provocator, Essedarius, Arbelas and Eques.

As I said:

Of course I did not use all gladiator types. But I believe you could classify all by this scheme.

I just did not want to spend so much time one the graphic, so I left out some types. To categorize all, there would have to be a 3rd group in the first step, with both offensively and defensively strong types, like the provocatores.
And there is the exeption of the Eques, where obviously a riding skill would be mandatory to train them.

They propose that all start out as Provocatores, then either advance to Scutarii or Parmularii and progress to Secutor or Retiarius respectively at the height of their advancement.

I do not agree with this proposal at all, since the provocator fights, should be much more skilled and elaborate than the ones of secutor and murmillo. The provoatores have much longer swords, which allows them to do fencing moves. Not just charging and stabbing like murmillo or secutor with their little toothpics. The perfect even match also speaks for advanced fencing skills, that were needed to get around an opponent, that perfectly knew your strength and weaknesses, since he wore the same armatura.

Iconography can be used to dispute this, but it does make a lot sense from a Trainers point of view.
Provocatores are a perfect Armatura to practise the handling of a weapon and shield combination useful for all Scutarii as well as Parmularii.

I strongly disagree. As stated before, you can train many fighting skills, like footwork and the art of falling correctly. But training everybody as provocator is just plain stupid.
First of all you have so many provocators, you will never be able to get all of them into arena fights. Secondly you will train them maybe a year or even more in a armatura, they will later not use again. This is wasted time AND money.
The benefits of training in a beginner's armatura are not as high, as being traing in your later armatura pretty much from the start. Most of the basic training, like fitness and basic movements (i.e. footwork and art of falling) can be trained by everybody together.
Fürthermore, in Vegetius, we learn that legionary start their fight training on the palus. You train on the palus not to improve you hitting strength, but to get an eye for the measure and better accuracy. If you start out as provocator on the palus and later become a staff-weaponed armatura, you will have to go back to the palus and relearn measure and accuracy. This again is a loss in time and money, as well as it is pretty embaracing for an "older" gladiator to train with all the beginners, I would assume.

The basic training of all new recruits might have been conducted in this Armatura, which also mirrors the typical Legionary fighting style. The Pectoral would also provide a measure of protection in early sparring fights.

What would be the use of mirroring a legionar ?

I agree on extra protection provided by the pectorale. I assume it was worn because of the longer swords and the high level of fencing the provocatores were capabale of. If this extra protection was not there, their fights could be over within seconds since with a sword and shield it is rather easy to open a way to the chest.