Mythics (and generally end-game gear) usually have ridiculously high skill point requirements that require you to build around the item itself and not the stats you want for your character. That means that to play the weapon you want, you're going to have to dedicate not only most of your skill points but also specific armor pieces to help you reach the required skill points to use it.
The problem comes in two parts: now that most of your skill points are gone, you're not going to be able to equip all armors you want. If you have mostly strength and dexterity, you probably will be forced to equip either way lower level gear or armors that follow that skill's 'philosophy' which usually makes it impossible to make an all rounder build (can't go for a defensive chestplate if all your points are gone in strength and dexterity). The second issue is that this usually results in you no longer putting skill points towards what you want your character to do, but towards items.
I understand the game is balanced around those requirements at the moment, but that doesn't stop it from being frustrating that I'm no longer putting skill points where I want my character's to be. On top of that, not all skills were created equal (agility and defense are not very popular for a reason), so being pushed to invest heavily in skills I do not want just because I'm looking for a specific MiD or piece of gear feels bad.
I don't know exactly how this could be fixed. Maybe toning it down so that you're not forced to dump 90+ skill points in a stat for a single item, but that would have big implications on balance since it would make a lot more builds possible.
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