Sorry for replying in English but it could be a few of many things due to all the updates. 

The attacker could have learned T3 attack or health in knowledge, learned reduced enemy health or defence, set the hero's skills with mercenary attack, could have legendary gems in their equipment, could have used boosts for enhanced reduction of your health or attack.

It used to used be down to military knowledge so it's best to look at the details part on the battle report to see the stats for the attackers boosts.

let see...

your t5 have a attack of 5537

his t3 have a attack of 5509

so, his t3 are almost as powerfull that your t5 in attack

you send 1012050 and he have 1234200 ... in attack power, it is 5.6b against 6.7b...you are on the loosing hand

if you was with the same amount of troop that him... 1234200 t5 against 1234200 t3, because your attack is 0.5% better, you will have win the battle...

of course, you will have win the battle but loss more influence because you will have loose t5 et he will have loose only t3... for a killing event, you will have won the battle but make less point that the ennemy...

Almost forget... you know the ennemy attack due to spy report... but you miss the defense and health value who are not anymore show due to crazy plarium update... if ennemy defense/attack was a lot more superior that yours, it will have be worse for you...

It is how it work when you are trapping with low level of troop... you try to attrack people to attack you with more high level troop and if you low level are good, same if they are all killed and loose the battle, you earn more point that you give for the event...

i have my t1 maxed everywhere, valkyrie included... cheap troop with a good punch and who give few point to the ennemi in event

below, a example of trap on tile with low level troop

more recent, using a dead city in our clan stronghold, trapping with reinforcement 800k t1 archer and 100k t1 spy

Libos Izzia said:

Why do you consider the values ​​of attack against assassins? These are melee troops! And because he has the characteristic melee attack if he has a melee squad and he does not appear to me despite having a melee squad!

well, i have no idea how are called melee troops in italian.... in fact, calculate yourself the attack power :

for you : AmountOfYourTroop * AttaccoControTypeOfEnnemyTroop

for him : AmountOfHisTroop * AttaccoControTypeOfYourTroop

who end up with the biggest result have the best attack power

my calculation of attack power :

for you : 1012050 * 5034 ( carnefice attaco ) = 5.09 bil

for him : 1234200 * 5446 ( attaco contro mischia ) = 6.72 bil

==> you loose, your are weaker in attack... his total attack power is 32% above yours

if you don't agree, it is ok but for me, rapport are normal as are the result of the battle... and don't count on plarium for explain how the game mechanic is put together

It looks like the defender, Cobalt 2270, with 9B influence may have had a garrison of T3 troops. 

Your max march is just over 1M and without a successful scouting report there is no way to know how many troops you faced. While a town in limited as to how many reinforcements it can hold you can have an unlimited amount of your own troops. 

I would suggest you try to onslaught the town so you have a better chance.

The new reports that plarium presents are basically useless, they don't show enemy reducer stats. Don't go ahead and determine if you will attack someone based on them, rather send t1 test stuff first before sending your best troops.

Most ppl are hung up on attack/defense/health stats, a dude could have those lower than yours but if his reducers are higher he will waste you without breaking a sweat. Past around 1000% of attack/defense/health give or take don't be stubborn and keep increasing miniscule percentage for large amount of influence, in contrast to that each percent of reducers is a big thing for your troops, so always go for that first then when it gets too expensive work on your stats. 

I will only assume that you didn't max ufls reducers, most ppl leave that for last if their ulf isn't lvl 60. Then your invader tree reducers. It would be helpful if you can share what Palace lvl that player was and what your Palace lvl is. Nowdays it's best to look at that and assume what your enemies reducers lvls might be. Based on his march size he looks like 30 or 31. 

Also I'd suggest going for t6 as fast as you can and not wasting time or money on maxing t5, they are sort of useless and give off points more easily.

MrClouder said:

... rather send t1 test stuff first before sending your best troops...

what i do since statistic for health/defense was removed from report... attack data alone is not enough info