ekko's numbers come to (in his basic combo) 120 (+10% ap) + 160 (+70% ap) + E (if there are 2 ranks: 80 + 20% ap or 110 if you skip W completely) + 100( passive = 10 + 10 per level + 80% ap) + base attack damage of 86 for a total of 536 + 1.7 AP
if we factor in thunderlords for 5 different sources of damage (passive, Q, Q, E bonus, auto atack damage), the entire combo comes to 626 + 1.9 AP or by level 9, let's say he has 65 AP, a random number for both of them based on reasonable value and build strengths
this comes to a grand total of 749 damage total, almost entirely in magic damage
annie, as you listed, will come to:
175(+80% AP)ult, + W 115(+85% ap)+ Q 220(+80% ap) as you put it 510 + 245% ap
since both are capable of using thunderlords efficiently, we could take a look at that
the efficient combo with annie will likely be:
Q 220(+80% ap)(for a guaranteed stunlock) + ult 175(+80% ap)(+ 40 and 40% ap for 2 seconds of exposure due to move speed unless they flash away) + W 115(+ 85% ap) + a second Q 220(+80% AP) and an auto attack thrown in (only 70 damage for annie) + thunderlords activation 90+ 20% ap
the grand total comes to: 930 + 385% ap
there is a big issue with this though in that Annie has no "basic" combo and instead only an incomplete combo for her damage variations
we can then look at ekko and say by some miracle he manages to pull this off
ult first at the beginning of his combo 200 + 130% ap and add an additional auto attack for another 86 comes to about 371, add that to ekko and his total comes to 1120
it's clear that annie has higher numbers in her total combo and will even survive his full burst, but why is it easier for ekko to pull off an assassination on annie than it is the other way around?
that is the bigger question