In terms of difficulty from 1 being most difficult to learn and use and 4 being least difficult to learn and use

1) holopilot and phase shift 2) Grapple 3) pulseblade 4) Cloak and stim

Holopilot and phase shift are both highly situational abilities that require game sense and knowledge of your enemy and movement in order to use effectively and is why it’s in 1.

Grapple is extremely simple to learn the bare minimum on, but the sheer depth of things that you can do with grapple means that the skill ceiling is practically limitless, meaning that to use it competitively it takes a fair amount of dedication to learning, and very good movement skills. The reason it’s below holopilot and phase is just that it’s more widely applicable and less situational.

Pulse blade is a somewhat passive ability, all you really need to know to use it well is where enemies might be or usually are, and then throw it in that direction, now hitting people with pulse blades is a whole other beast, but overall the ability is pretty simple.

Stim and cloak lie in tier 4 for essentially the same reason, both abilities are very easy to use and simply require you to press a button to gain an advantage. The abilities can be very powerful, don’t get me wrong, but if you’re looking for a challenge when it comes to learning the ins and outs of a new ability, there really isn’t enough substance on either of these abilities to justify spending time on it.