I’m not really a high level player and certainly pretty far from hitting a wall on 14 star titans, but i think a “no strong/weak” element titan is pointless. It would just be an excuse/opportunity to just use heroes with the most op skills without limit.
Instead, I’d suggest that at high levels the area on the map in which a titan spawns has an effect during the battle. Maybe over forest terrain every titan attack has a chance to spawn a juiced up minion, but like an elite enemy with mana and an ability like the boss fight side minions, and the sea could have titan attacks raise a fog slowing your mana gen, and a desert having dust storms that randomly drop accuracy, and volcanoes an attack debuff from a burning effect. The “terrain effects” could be tied to an element as well, and when the titan moves/spawns into terrain with a matching element then it could gain a buff during that battle/apply a debuff to certain opposing elements, encouraging alliances to attack when the titan is in the most favorable terrain.
As for a champions league, i feel like the higher tiers have enough carrots for advanced players - challenge event placings, national/global public leaderboards, alliance rankings. It kind of already feels like the highest level players are in a league of their own, at least to me in low diamond. Not sure what a higher league would offer to a player at that level anyway tbh, other than a relatively paltry chest loot improvement