Dan I agree and disagree with portions of what you said. Honestly your assesment makes sense based upon the past where you first participated in Beta in the level 9 and under room.
What you didn't take into account is that there are quite a few players in the level 9 and under room that have purchased boxes as well and will ruin your streak because they are experienced players choosing different Sphere's and starting fresh with their new starter a la Lawtia's dominance gained popularity.
I admit it was still easy to win the majority of the matches when I restarted all three times from Refess > Gowen > Falkow > Lawtia. I would run into a stacked card file every so often which would ruin whatever streak I was on. When I played with Lawtia my hardest match up was versus other Lawtia users who had purchased cards in the level 9 and under Arena. Zombie Lord is tough to deal with when you aren't expecting to see him from a level 1-3 player.
Mainly its the soul cards that are killers though. Good luck to you if you try to do it yourself. Maybe the timing will be better for you than I. You only have room for 45 wins before you switch to level 10 rooms. A 30 win streak is 2/3 your wins. Possible, yet you're strategy revolves around being undefeated which suggests that you have to be unbeatable for it to work. Should a game need such dominance just to stay alive at the +10 Arena? Seems like a terrible way to keep players around. Sure some will buy cards. I honestly don't understand how the fan base got so large in Japan unless it was extremely cheap to purchase cards.
I've heard many people say they've spent $50-100 for cards from Alteil. I'm happy for the makers as their hard work is probably deserving of this. On the other hand that is quite a bit of money to pay up front for a game like this. To each his/her own.
Good luck and have fun with it...