One thing to keep in mind is that currently much lower level players can also “easily” win a league with lots of higher level players - in fact that happens to me every now and then (where I am the much stronger player that loses against some low level player).
Let me explain why:
Leagues are about medals, which can be gained by attacks. The stronger* the base you attack, and the weaker* your own attack value is, the more medals you can gain from that attack if you win. Also, more attacks = more medals.
Thus, by spending gems for scrolls or food and/or watching free food videos, players can increase their medal gain dramatically (given, they use enough gems/videos), no matter whether they are high or low level players.
Sure, a weaker* player gets on average less medals per attack, but with decent raiding skills they can also win attacks on slightly stronger* players easily, while players high up in leaderboard might even have to scroll on same-level players to get a 100%. Also, as already often mentioned, lower players need less bread per attack and thus can do more attacks when levelling up their farms properly.
Currently, I have an account with lvl 80 king, relatively good equipment (all gold/legendary items) and almost-max spells at about 3800-3900 trophies. And I’d say my raiding skills are decent, too. Though, recently I often struggle with bases giving me like 300-400 medals. On the other hand, I have access to an account with lvl 60 or so king that has a lot weaker gear (blue, purple, gold, some quite outdated) and by far lower spells, and also by far lower troop levels, and that account currently is around 2300 trophies. On that account, I can win most battles against enemies that give me 300-400 trophies or even a bit more although I am less comfortable with the device and not familiar with that hero stats and troop combinations (thus, my “raiding strength / skills” on that account are definitely not better than on my account, but rather worse). Also, the owner of that account has definitely worse raiding skills than me, but still wins more diamond league tournaments than me in recent weeks (without using any gems on scrolls or food either).
When I was at that level (and also a lot weaker than now, of course) myself, I also won a lot more diamond leagues than now, by the way.
The reason why some high level players win their leagues may be they invest gems in food. Not everyone, of course, but some definitely do that. Especially all those high or elite level players breaking league records all buy tons of food for that and spend many, many hours with raiding dozens hundreds of times. So it is not like they just accomplish all that easily without effort.
Also, e.g. Vanguard Legion is known for having players that spend tons of gems, not just on food but on the actual attacks. I have heard of some spending like 50 gems per attack for scrolls even on relatively easy bases… when these guys manage to win their league, I guess their reward is a lot less than their cost to do so. (@Vanguard Legion: No offense intended here, just saying.)
(*) One note on “strength”: The actual strength of a base or player and the strength that the matchmaking/loot computation system assumes is not the same. And in fact these two “values” can differ a lot!
E.g. players with more trophies are thought to be stronger, lower trophy players weaker. Also, rather than judging the actual strength, the “success based” strength is judged (e.g. outcome of recent battles).
I notice this a lot recently, when getting opponents from matchmaking that have way stronger bases than me. I can barely beat those (or not beat them at all), even with decent attack skills and strategies, as they have all highlevel or max lvl towers and more moral points in their waves than me, while my towers are much lower and the main difficulty of my base usually lies in a clever layout and troop combination.
If I still win those bases (due to them having a bad layout, or due to me being a great attacker, or both), then I just raise up further in trophies and also am seen even stronger from the matchmaking system (higher trophies + success in raid), despite I am not stronger at all. This lowers the amount of medals I gain for hard enemies and lowers my chances for successful raiding.
Just to give you an example of what this means: Recently I raided a base with all max level towers, max level troops/monsters, very high level troop waves, some elite boosts, 1000 more trophies than me, but a very bad layout. I managed to get something between 65-70% in that base (running out of time at the gate, but with 33% to 50% of gate health down). Still, I lost like 5 trophies or so, and got only around 300 medals. In comparison, my towers have on average maybe lvl 3-4, those towers were on average lvl 9 (max lvl). With a proper layout I wouldn’t have had any chance at all and probably have needed like 6 scrolls/resurrects to get to the gate. Still the loot system decided that me almost bringing down the gate (and killing like everything else in that base) wasn’t worth any trophies, even was worth a loss in trophies for my “bad raid”. I think that tells a lot…
Maybe you still remember top players complaining about trophy stripping where other players with 1k less trophies got like +50 trophies for worse results?
In other words, actual strength + skill + success are thrown together for the matchmaking algorithm, making my life harder due to my recent success, and making it easier for players with less skills and thus recent failure.