Forgotten Tales

For lv100+, 1 Arm Point adds HP=100^1.3x0.5=199 to max life. 1 Dex point reduces mana damage by 1. So it's good to add dex when opponent can cast 199 spells, and u can take 199 spells.

199x5-150(from gear)=845 mana
Due to mana regen, just count it as 750 mana. That means opponent is about lv400
Spell Damage= 50+2.5x750=1925
Assume u are a lv400 archer, u set your dex as 200 for pvm
Total Spell Damage= (1925-200)*199=343k hp
Assume that you've put all points in Arm, Your HP=100^1.3x(5+0.5x600)+50x300=136k HP

The results is kind of weird, anything wrong?

First, if you're saying high level mages are overpowered compared to others right now, I agree...

Ok, with that said, let's look at the numbers
I double checked all your math (no offense intended LOL) and checks out as far I see, spot on -- however, there are three things i would like to point out. ..

1> your level 400 mage (750 mana, 50arm) has slightly less than 18,000 HP, so he's in danger from much, much lower level mages (he'd have to be impossibly fast on heal spell to survive attack)

2> I think you missed spell effects being cut in half during PvP... this will change the numbers... your archer was dead in 79 casts, or 13.2 seconds... with spell damage cut in half, this changes to 178 casts, or about 30 seconds ( 1925/2 -200 = 762 damage per cast) ... this will use about 890 mana, which with gear and regen is probably just about max

3> obviously, this archer is useless with no strength... I'm just pointing that out so nobody else has LOL

Anyway, to be honest, I'm not exactly sure what you were saying/asking, but i enjoy figuring this stuff anyway ... and that is a really interesting point about the dex being more beneficial at some point... I just ran similar numbers with my mage on arm vs. Dex against monsters (dex better against southernsun mushymen and spectre wizards, arm better against most other stuff at my level BTW )

actually, I'm thinking is it really worth putting points in dex although dex reduces mana damage

Ahh, ok.... my opinion is no. Worry about dex for PvM, and for PvP against other non-mages if you expect a lot of it, but vs. mage it's a point wasted which could have been helping you grind if it was a point in str... That's my two cents