Let me be more fair, I guess...
On paper the new matchmaking and league systems sound good but they require a large active player base that does not exist at the moment.
Without addressing that, this sneak peak provides nothing promising.
Ideas to drive up arena activity:
Make fighting in the arena free, i.e. remove tickets. But matches would give only rating points.
Remove "demand all modes" button.
Purchasable items "(Great) Gladiator Elixir" with increased prices will increase the rating points by a specified percentage and additionally give arena points in the value of 100%-150% of rating points.
Rating points count towards rankings, technically you should be able to climb to the top league ranks for free! Well, time and probably a whole lot of top-tier buffs make it not so free...
Depending on how players spread in the new leagues, top 50% or so of active players ranks will also get a chunk of arena points at the end of the season. Could be a certain % of the rating points, depending on their league.
Arena points/shop:
Arena shop items that are more frequently updated with items that are relevant not only for arena but also for mass fights, items such as anti-control foods or anti-resistance buffs for example, or special minions with AoE effects. As far as I know, most if not all AoE skills from minions were removed at one point, so they would be very expensive, but also unique. This is important for end-game players of the top guilds fighting in raid boss wars and such, it will keep arena relevant for them forever basically.
For newer players, get rid of the chests, add the costumes to be directly purchasable, and the books too but make them cost something crazy like 500k AP or something. People Like to work and grind towards a set-in-stone goal in MMOs... Add more books too, why not.
Rewards for new league rankings can be whatever but ideally, the top league would give seasonal buffs that contribute to mass battles.