If your opponent’s sum of TP and your sum TP is in 5000 range, I would say it’s not a mismatch, as a basic check.
Not winning the game doesn’t imply it’s a mismatch. And not winning happens when - you don’t use all flags, you waste your flags on wrong target (overconfident and then score poor), not working in tandems - competing against each other and not thinking about targets and maybe scoring more.
Basically, if you don’t do something like this: Alliance War Strategy Guide (except 'have 30 maxed 4/5 star heroes - not needed for lower,and mid power alliances - you need stacking colour skills and maxed 3 stars and 3.60 for 4 stars - will get you a long way), and you’re in some ok range considering the TP, then you lost because your opponent had better strategy, even if it means - they used all flags, and you had 3 players on vacation.
Match is done by heroes, and yes, there are few border cases - those who bought 5 stars and keep them unleveled will get matched against maxed 3stars and probably get smacked. However, game is about average player in average alliance. If alliance has too big disparity - eg players between 500 and 2500 cups, then yes, matches will probably be mismatched.
Expecting that devs cover all weird scenarios and whining it’s a mismatch because of that, I just don’t buy it.
No, screenshots of end result isn’t a proof - state of the field, and complete logs of the play would be starting points.
My experience is that huge amount of alliances have no clue about strategy.
Those who have SOME strategy - will score better.
If alliance is in top 100, that just means they’re smacking titan and doing raids, they also don’t all have hundreds of maxed 5 stars. No, they usually can use 3 flags decently, and then it’s ‘let’s see what happens’.
Currently, war is won in last three flags - the smarter you do use them, the better is the score.