Its just that price is not right, and the release schedule.
I would have bought a decently priced colisuem dlc with 20-30 cool fights included, possibly with a nice story dlc released at the same time to make use of the monsters.
But if this keeps on you gonna pay a shitload of money for a couple of costumes and some new monsters in your party. I am even wondering who is supposed to buy the costumes that come out in a couple of weeks because most people that were interest in the game have completed it for a long time by then and will have moved on to something new ...
I definitely agree that a full Coliseum DLC at 10-15 dollars would be much more worthwhile (and would probably sell more) if it contained a bunch of fights in a set with extra Fragments, and achievements/trophies.
It doesn't even have to be 20-30 unique fights, but if they had like 5-10 brand new boss fights (like the current ones being sold via DLC), and then added put them at the end of Challenge Tiers mixed with fights consisting of unique synergy groupings of existing enemies.
Like an existing strong COM enemy with tons of HP, paired with 2 smaller MEDs and 2 medium RAVs, or all the different Chocobo colors in a single battle, or Chaos Bahamut + Twilight Odin, etc. There are a lot of creative ideas you can come up with for interesting arena battles even using the current game's assets. It would add an extra layer of challenge and fun for palyers, instead of just being cash-in DLC.
It's too bad S-E is kinda new to this concept and they don't seem very mature in their DLC planning.