your biggest mistake in regard to artifacts is focusing too much on using matching sets. getting a set bonus is helpful, but it's far more important to use pieces of equipment with good main and substats even if you have to pull them from different sets. in the case of artak, you will most likely want crit rate gauntlets, hp% chestplate and speed boots, with as many substats as possible giving hp, accuracy, speed, and crit stats.

i dont think relentless is terrible on artak , i wouldnt really say you did it "completely wrong" could he be geared in something different?sure. not sure if id personally put crit rate gaunts on him like the guy above said though, mines built in 2 x immortal sets and i think 1 x perception or speed set and hes around 85k hp, 3100 def, 220 speed, 270 res, 285 accuracy and even without crit gaunts he has 40% crit rate and 105% crit dmg, but as the guy above said you can even go down the route of not using any item sets, and just aiming for pure stats on all items regardless of what set they are from.

i dont expect you to be able to hit the stats i did on my artak as you are still in the early game stages,so just set ur self lower targets to hit, the one main thing wrong with ur artak tho is his speed is 117, this is really low, and he could probably have more hp/def.

No, you're not doing things wrong - getting better artifacts is all part of the progression. And absolutely ignore the "in-game advice" for artifact sets, because it's plain wrong and broken and is never worth referring to.

The only thing I would suggest is not to take anything under 5* to anything more than 12 - those accessories are the one obvious flag I see, as it's usually not worth powering up 3-4 star accessories. Just keep farming Spider 10 until you get better ones.

One thing to keep in mind when you are seeing videos of people blowing up things with someone like Artak is that they probably have a fully loaded Great Hall and have masteries in place. I am not sure where you are at on masteries with Artak but I know just how much of a slog it is to get your first few champions maxed out. Those things matter.  Books really help Artak also. 

It sounds like we probably have another free legendary on the way that I am sure will help. You are lacking a good rezzer unless I am missing something. In the absence of that I would suggest taking Appacathary up to 50 to help keep your team alive and give you a speed boost to boot. Conellia can heal and heal well but putting your primary damage dealer to sleep may be more harmful than beneficial in the long run.

Long story less long, you have a road ahead of you. The key is knowing where best to spend your resources. Artak, High K. and Appacathary are champions that will last you well into mid game. Don't feed those champions to other champions. I wouldn't take anyone else other than High K. up to 60 on your roster at this point.

Melga with hit points, def, & speed will take you a long way.

Totally missed Melga. 

Thanks all the Good saved me a ton of stress and time much appreciated!!!.