First of all, I'm under the feeling that you're somehow insulted by my previous post. If that's true, it was by no means intented.
Now, there are 2 ways to play this game. One is to level up, complete the storylines, basicly play in "single-player" mode, where (excluding trading) you only interact and fight with the game generated enemies. Second way is the competitive one. The player basicly picks a tier, lock their XP there and max their capabilities, in order to compete against other players (PvP) for castles, guild outposts, fame, etc. I won't say any one of the two is better than the other, people that belong in the 2nd category though, tend to have stronger gear, more solid fighting tactics and better allocated stats. In my personal opinion, competitive play requires more tactical thought, more "skill", if you'd prefer the expression, and ofcourse more resources.
So, to answer your question, what I call "decent" is people that use their given resources in the best of their ability.
Let me explain. A rare (blue) level 49 Dark Follower Archer (the base enemy with the highest agility and dexterity multipliers in tier 5) has 196 Agility and 196 Dexterity. Your 2nd screenshot shows me that the guy you linked is a Dark Mystic, since his stats are similar to the ones of his portrait, thus unbuffed. Using level 7 Blur and Poison Cloud on that monster lowers its stats to 146 of each. 425 Agility offers nothing more than, let's say 245, against 146 dexterity. since his chance to evade is capped at 75% - 1 out of 4 attacks will hit no matter if your agility is infinite. His 120 dexterity will still miss half the time against 146 agility. So, by putting 120 points on his dexterity, rather his agility, he'd max his chance to hit too (75%, or 3 our of 4) and also raise his critical chance by 12%. He'd deal more damage, finish fights faster, use less spirit in fights for heal spells, use less spirit potions between fights and thus make his life easier.
That would be more of a decent mystic to my eyes, using the same resources he now does, but in a better way.
P.S.1: Click
here to see all the available sets and their bonuses.
P.S.2: Using diamonds is by no means cheating. It's the way the company that created this game can keep it up and running.