A good SP system can make or break an RPG- especially a PVPMMORPG.
Dust had a terrible system that made breaking into the game too hard, but rewards came quickly. Still, the tree expanded vertically rather than horizontally and we did not enjoy. The passive UA-SP was nice but the active made it a grind which we did not like. We should play for ISK, not SP.

Eve had a better system. Lots of options, but still plagued by the five point level system and having to log in every few days to schedule skills is annoying; plus the best gear takes years to obtain- not something good for a shooter. SP should never be a motivation over the desire to just shoot stuff.

A better SP system would take the worst of the two out.
First off, the tree expands much more horizontally. Nothing is an SP sink, because every single weapon, vehicle, tool, salvage, drone, etc has a lot a lot a lot of unique skill associated with it. For example, salvaging for ship parts from a fallen cruiser at 100% efficiency is huge, but speccing for that will mean your ability to salvage charred drop suit energy cores is at 1%. This means that at 100%, efficiency, one salvage will return one item that is working at 50% capacity (efficiency(0.5)) and with 100% of the parts, so a Legionnaire could salvage a working cruiser by himself, given time, and turn around to sell a working cruiser to a Capsuleer at a huge discount because it cost him so little to salvage compared to the cost to manufacture one Eve-side. But that's just salvage.

Every weapon has a huge number of modifiers, but they're specific to the Legionaries abilities when using the weapon class (WC; referring to shoulder fire, single shot/ shoulder fire full auto/ SF-burst/ hip fire burst/ HF-Single shot/ wrist fire auto/ wirst fire SS/ large precision turret/ large enfilade turret/etc)rather than a flat damage buff. This includes, but is not limited to: reload speed, hip dispersion, ability to ads faster, movement speed while carrying the weapon, scope sway, stability when firing, ability to field strip and repair a broken weapon efficiently and properly, and everything else that affects the user's ability to handle a weapon, but not the weapon itself.

Above specific weapon type there is general weapons handling which would affect multiple weapon types (shoulder fired/ worst fired/ semi auto/ bolt action/ burst fire/ full auto/ explosive / HbR/ HbP/ laser/ thermal/ kinetic/ nuclear/ EM/etc). These encompass not just a small group of weapons, but many seemingly unrelated weapon. For instance, speccing high explosive+semi auto + wrist fire would give a big bonus to a wrist rocket sidearm but still carry over to anything that fit those descriptions so a nerf is not as painful as in dust because you spec one gun; this way, every skill point earned affects many things so everything stays relevant while still allowing the ability to specialize.

Beyond that, skill points are earned over time, and are more accurately measured in minutes than anything else. Investing time into any skill does not affect someone's ability to operate something past the first minute (one minute to be able to operate ANYTHING, but it does play a huge role in determining if that person can fit more than a small blaster turret on a Madrugar or if that turret will even fire straight for more than a second. What this all means is you start your journey as a worthless, untrained boot who can't do anything well, but can pick up anything and use it.