Here is the damage comparison between a level 61 pure STR/AGI player against a level 1 player and how AP plays its role in reducing damage.

level 61 player hitting level 1 player

Melee/Range Attack

Defense* ... 1st attack** ... 2nd attack ... 3rd attack

18 - 69 ... -4HP,-4.5AP ... -8HP,-0AP ... -6HP,-4.5AP
37 - 69 ... -9HP,-9.5AP ... -18HP,-0AP ... -14HP,-9.5AP
74 - 69 ... -17HP,-20AP ... -34HP,-0AP ... -26HP,-20AP
146 - 69 ... -35HP,-41AP ... -70HP,-0AP ... -52HP,-41AP
294 - 69 ... -70HP,-80AP ... -140HP,-0AP ... -105HP,-82AP

18 - 6 ... -4.5HP,-4.5AP ... -9HP,-0AP ... -7HP,-4.5AP
37 - 6 ... -9.5HP,-9.5AP ... -19HP,-0AP ... -14HP,-9.5AP
74 - 6 ... -19HP,-20AP ... -38HP,-0AP ... -29HP,-20AP
146 - 6 ... -40HP,-41AP ... -80HP,-0AP ... -60HP,-41AP
294 - 6 ... -79HP,-80AP ... -158HP,-0AP ... -118HP,-82AP

* The stats of the level 1 player.
** The damage ratio of the attack. eg. damage you see is 40 = -20HP,-22.5AP.

Although the Defense and HP values keep changing, the AP reduce at a FIXED rate according to the damage received. The Lv 61player does not have any outstanding advantage in depleting the AP of a lv 1 player. Therfore lv difference is not a factor on reducing the AP.

This shows that higher damage depletes more AP. When depleting AP, the damage is reduce by up to 50% as seen in the difference between the 1st and 2nd attack. So watch out for the 2nd attack in PK cuz AP does not work in the 2nd, 4th, 6th, 8th hit which you'll get damaged more. Especially if the katana lands a critical at the 2nd hit for 1 hit KOs. When AP is 0, then ALL hits will be like the 2nd attack, doubled damage.

Now let us see the reverse side, level 1 player hitting level 61 player

Melee/Range Attack

Defense* ... 1st attack ... 2nd attack ... 3rd attack

18 - 310 ... -1HP,-4.5AP ... ?,-0AP ... -1HP,-4.5AP ( '?' = mark means small random damage)
37 - 310 ... -1HP,-9.5AP ... ?,-0AP ... -1HP,-9.5AP
74 - 310 ... -1.5HP,-20AP ... ?,-0AP ... -2HP,-20AP
146 - 310 ... -3.5HP,-41AP ... ?,-0AP ... -5HP,-41AP

18 - 730 ... -1HP,-4.5AP ... ?,-0AP ... -1HP,-4.5AP
37 - 730 ... -1HP,-9.5AP ... ?,-0AP ... -1HP,-9.5AP
74 - 730 ... -1.5HP,-20AP ... ?,-0AP ... -2HP,-20AP
146 - 730 ... -3.5HP,-41AP ... ?,-0AP ... -5HP,-41AP

18 - 1138+ ... -1HP,-4.5AP ... ?,-0AP ... -1HP,-4.5AP
37 - 1138+ ... -1HP,-9.5AP ... ?,-0AP ... -1HP,-9.5AP
74 - 1138+ ... -1.5HP,-20AP ... ?,-0AP ... -2HP,-20AP
146 - 1138+ ... -3.5HP,-41AP ... ?,-0AP ... -5HP,-41AP

*The stats of the level 61 player.

Note : level 1 player max attack can achieve is 260 using a normal +9 weapon and with maximum point PU.

As we can see, the damage on AP is the same on both sides so LEVEL difference does not give neither player ANY advantage.

Therefore according to the ratios above, you'll have level 61 player doing 1 hit KO on the level 1 player.The level 1 player however will deplete the level 61's AP to 0 but the lv 61 player's HP won't reduced much.

This why we see level 5x players dealing a godlike 4x,xxx damage on low level players and the low level player will see both AP and HP turn to 0 in one hit.

IMPORTANT : when in Meditating mode, you will lose HP at a 150% rate than in standing modes.