they can hit towers or units in city, but they still bypass city defense bonus all together
if u throw assassin on some alt city with zero towers zero walls zero decoration, you get more or less same pvp points as hitting someone with full developed city with city defense bonus of 90%+
if u manage to get down towers with assassins, yes your raid will by doing more dmg, since towers are down.
but question remains, why assassins are so bugged?
unless u can prove otherwise they do around 15k dmg, 12.6k is advertised
they do ignore city defense bonus lets say +90%(yes they can hit towers, but that's different) otherwise they would do around 7k dmg from 12.6k but this point kind of make sense, since they sneak past city defenses
their overpowered dmg does not make sense.
reason why your jav survives 90% of time in friends cities is that people have defenses there! and if total def number is greater than lets say 15k facing 15k dmg from assassin, will result slightly under 50% loss for defended. In theory your jav will survive. simply statistically speaking. But more defenses that guy have higher chance of your jav surviving. And if they have just few units, then yes towers will soak 250k dmg each and units rest of it.
now to your point, where u again claiming infinite waves of 10 assassins wont do anything.... like really?:)
lets imagine city is defended by 150million defence, lets say 500 thousands units in total.
wave of 10 assassins hit, odds that tower will die is very small like 20 in 500k, but in very unlikely scenario 2 PA can indeed kill all 20 towers even if there is 150 mil defense, but odds are astronomically small.
wave of 10 PA will do around 126k-150k dmg, doesn't matter your personal loses or opinions, cca 126k-150k defense will die, now we have only 149,85mil defenses
1 player can repeat process 9 more times,
so 1 player per day can inflict about 1.5mil dmg, reducing total def to about 148.5mil
reason why I picked up so nice number to show, that 100 players sending each 100 assassins in one day (10x wave of 10) will in fact fully wipe city with 150 mil defenses
that's kind of is in conflict with your statement "they wont do anything", which I have proven they will in fact completely wipe out entire defense in that city.
Ofc nobody ever seen 100 players throwing 100 assassins at one city in one day, but that's outcome you would get.
and more importantly same damage applies to smaller scale with smaller defences in players cities, where handful of PAs will unfavorably kill defender units and give him about 1/5 of pvp points, he should get.
lets not confuse ourselves with sending assassins in waves and ordinary units in waves, assassins do full dmg and can hit champions with just total of them is 1, each single assassin work independently and will always do full dmg vs random units.
with old battle formula people sending small waves would net smaller units killed than it is now.
but still it wasn't zero just small portion of what it is today, today you more of less kill as much def as you send off, if u hit lvl 5 pan with 100swords, you might kill 1horse, 2 phalanx, few lower tier units. Unless you mass certain amount of attack force you wont be able to kill any champions, if ofcourse you don't run thousands of waves, which would gradually wear down supporting units until only champions left.
That's quite different with assassins , they can hit any unit,champion or not, they do ignore city defense bonus and they do inflict more than advertised dmg.
That's why people doesn't like them, they are overpowered(or their tooltip show lower numbers vs reality) and are bugged.