These have mostly been jokes, with me as the butt of them. Even using the booster tower I'm pathetically overmatched. I hate it when something like Heroic Race has "win league battles". When I see that it's like, ok, that's the end of that contest: bummer.

You can reset the league battles to get a new set of opponents, if that helps. But your problem is common enough. Most players go through a time where leagues are difficult to win. The prevention is to not level up your game too quickly. It is tempting to play leagues frequently for the rewards, but this puts you against stronger and stronger teams as you progress.
The solution is to improve your dragons. Feed, train and empower your heroic and legendary dragons. In particular choose a team of at least 3 (to start, but more later) dragons that have a wide range of elements and that have strong attacks. Get these as strong as you can as quickly as you can. League battles have opponents capped at level 40, but you can use level 70 against them. Once you have a strong team that can critically attack most opponents with one of your chosen dragons, you will be on your way to invincibility.
I am long past this stage and have been using leagues for a long time now to rank up dragons from C to A+. I use L70 Kratus and Supersonic and switch the newbie in to get credit for the kill. My baby account, level 97, uses high arcane as the first fighter because it cannot be critically hit.
I hope something in this helps you. Good luck.

@susan-mclaughlin Thanks. I can sigh in relief and wait.

me too, i'm stuck always at win league battles but thankfully others are too haha. I don't know why every time I match against strong heroic dragons or empowered legendary dragons or dragons with no weaknesses. But I guess it's part of growing and becoming stronger.

@susan-mclaughlin i did not know that league opponents are capped at lvl 40. i use leagues to train new dragons too and only see lvl 40 enemies, but i thought thats because i keep my league low by always resetting before the last fight.

is there no difference in opponents between league 200 and league 400?

@apoli
I believe that league battles are matched against player level, no matter what league you are in. The opponents are capped at level 40 but they can still use their 5 stars.
The trick is to have that strong team of 3 to rely on. Choose dragons that will be easy to get orbs to empower. I had 5 star kratus from before breeding was reborn. And I bred and fed 20 supersonics in the sanctuary for recalling 100 orbs each. You might trade for orbs, and use your arenas to get orbs for boulder kitsune etc.
Your practise of resetting leagues may simply be depriving you of the rewards you win for completing each league. I'm not sure there is a benefit for remaining low like you are.

@apoli said in League battles:

is there no difference in opponents between league 200 and league 400?

No. There is no difference.

mind blown! thanks you two! i never stop learning.

I'm just going to quickly post here my best advice for improving dragons:
Choose 3-5 legendary or heroic dragons that you can more easily get orbs for empowering. It is best if they have a wide range of elements among them so they can critically attack most dragons.
Train them to improve their attacks.
Empower them.
Feed them to max.
Do not use them for building towers.
Do use them for friend challenges and quest battles to get them to A+.

I'm also going to post here what advice I use and give for improving dragons for arenas, once you have leagues under control:
"During each arena season, choose dragons of only that element for feeding. Choose only legendary and heroic dragons, and perhaps highly empowered epics. Choose only these dragons for quests and friend challenges. If you can, choose one for leagues if you have 2 other powerful dragons to take the heavy hits and trade in the improver to make the final kills and get the ranking credit.
Do not put these dragons into training or empowering or tower-building because they won't be available for battles or feeding.
When the next season starts, change your quest battle lineup to dragons of the new element, and feed those dragons. You can go back to train and empower dragons of the previous element again.
Eventually, slowly but surely, you will build stronger teams of dragons for each element."

still thinking about leagues. what happens after the last battle in league 400? does it automatically restart and refill the battles?

@apoli It stays at 400. Nothing changes.

It would be cool that it goes down a few levels, considering that the dragons at lvl 40 already have heroics.