Coloseum Pay-Wall

As Seedy states, the progression barriers are deliberate. 

Last Era, I regularly used crystals to buy more and more Era Level Currency (never obtained any materials), but all this ever achieved was pushing me against the progression barrier earlier than those using little or no crystals. I think your summary here: 

thekustosh wrote:

I even started to think that this ridiculous Era system that CG came up with works in such a way that if someone spends some money at the beginning and then stops, they are basically forced to wait until completely free-to-play players catch up to their stage before they can start getting anything better from the bosses.

is pretty much bang on how it works.