I wouldn’t say it’s useless, you just need to invest heavily in double punch attribute to make the best out of it/make it worthwhile. Double punch is basically a better replacement for your auto attack, and if you have good ping, you’d be able to punch faster than you can auto attack.
Every 5 levels of double punch is 5 * 35 = 175 skill damage lost, which doesn’t look like a big deal compared to the weapon damage you could have with transcended 330 gear. If you pull some numbers anyway:
175 * 1.5(crit) * 1.3(double punch debuff) * 2(attribute) * 2 (two punches)
= 1365 damage
So each circle of monk gives you 1365 more damage (agaisnt cloth, strike would be 1890, leather and ghost 1102) on your double punch assuming it’s maxed attribute and you trigger the debuff. This number is only really significant if you can punch pretty fast IMO, like 2-3 casts per second or korean net fast.
I believe the main bulk of the damage is going to come from either having a trasncended level cap weapon or a very high enhanced, transcended toy hammer to make things explode (I can’t confirm it but from all of the media I’ve seen and personal experience, explosion works out to something like 5 ticks of 400~450% of your phys damage).
So monk 1 is not a bad pick for a pally to inquisitor build IMO. However, all it’s going to offer is better single target on boss, filler for breaking wheel if you’ve used up all your skills and things are still alive (probably only have the extra time to actually get out punches at inquisitor c2 or c3), short armor break (around 6 seconds), and 1 tick per 2 seconds bleed (helps with toy hammer).
Assuming inquisitor skills stay at medium to high levels of CD time, you’re going to inevitably have downtime with your skills going pally3 where you have nothing worthwhile to use. If the boss you’re fighting has lots of attacks to dodge though, that could be less of an issue.
As for plague doctor, you’re getting bloodletting (can be made redundant by dispellers in PvE until they make level 2 debuffs more common, miko charms that are lv2 debuff dispellers are 1000 each to craft whereas dispellers are 400 each, so it helps you save money at least), healing factor (very good assuming you’re not letting yourself get smashed on by tons of mobs on purpose), potentially pandemic (although you yourself don’t have much use for it), and incineration.
Incineration, even though it’s magic, isn’t that bad at the moment for a physical build. 1091 skill atk at lv5, 532 mag atk from the 315 purple mace, and 330 mag atk from being level 330 means:
1953 * 2(attribute) = 3906
Ticks at least twice a second so 7812 a second agaisnt most elements. 11718 agaisnt ice, 3906 agaisnt fire, multiply by 1.5 if enemy is ghost type. Agni necklace more or less will double the output, but I question wearing it solely for incineration…
Duration is 5 secs at lv5 and +2 seconds for each debuff on the enemy, and requires at least one debuff.
At pally3, you have about a max of 3 debuffs on your own (the magic inquisitor skill, conviction, deprotected zone which isn’t worth casting IMO), so forgetting deprotected zone you have 9 secs per use solo, add both because 2 overheats means you can keep it on for 18 seconds by yourself with an 11 sec downtime.
That’s less of an issue in parties where there’s no other plague doctor, but don’t dream of being able to use it on world bosses unless you’re purposely sabotaging another plague doctor (in which case you don’t have plague vapours).
The problem I have with incineration is that it’s magic, and as a physical build, you’re going to be transcending a physical main stat weapon which will leave your mag atk in the dust. Thus, as the level cap increases, so does the gap.
At the moment, assuming the boss isn’t ice, fire, ghost, strike or leather, it’s 15626 for incineration (with agni neck) vs 18525 per cast of double punch with 2000 phys atk (a highly transcended weapon). Incineration can tick while you use your other skills, but if your ping allows for it you can double punch more than once a second, which is going to outclass incineration if you are able to stand next to the boss safely.
It really depends on the scenario to be able to say which is better, but unless they release agni rings, it’s safe to say that incineration is hardly going to be able to improve as more caps are introduced, whilst double punch is always going to benefit from transcending your current weapon. There’s also the issue of double punch attribute costs 61 mil to max and incineration attribute costs 86 mil. I personally wouldn’t invest that much in a skill that isn’t my main dmg type but the decision ultimately lies with you.