Removing the SP cap will only harm Dust in the long run, there's no denying this. Doing so will allow players who have the ability to play 8+ hours a day 5+ days of the week to accumulate SP at an alarming rate. Since there is no limit to how many skill points you can accumulate total nor how many skills you can learn it only makes sense that it won't be long before every skill available has been learned by the aforementioned players. While it's true that individual skill and tactics do play a part in battles, it is even more true that skills and equipment play a bigger part.

Now what will happen when Corp A's players, who put in 56+ hours a week into the game and have eventually learned every skill play Corp B whose players can only play ~14 hours a week? The latter corp could have Sun Tzu pulling the strings for them, but it won't make a difference when Corp As players have more armor, do more damage, regenerate shields quicker, have more accurate guns, and all have prototype-level gear. It won't make a difference when any member of Corp A can call in a tank or a dropship until the vehicle limit is reached while only a few players in Corp B have the weaponry or the vehicles to counter it. And then, because they had to specialize to use those items and cannot cope with Corp A when they all switch to a different loadout. Not to mention the intangible benefits of being more familiar with the games mechanics, and therefore having refined control over your character.

When it hits critical mass, there will be a few elite corps who will battle each other because no competition can be had from the other corps who can't put in the time the elites can. The normal players will stop playing the game because they'll constantly run into enemies they can't kill, and the elite players will either stop playing because they no longer have a challenge save for the few other elite players, or they will continue terrorizing new players until only the elite are left.

It's easy to make the comparison with EVE in that new players can be annihilated by the veterans but the game still thrives, but if everything was wiped clean and every EVE player started from scratch, would the few players who can play constantly have Titans within months? That couldn't happen thanks to EVE's restrictive skill system. But with Dust, SP is gained actively, there is a very distinct and tangible advantage to be gained by playing often if no SP cap is in place. It's one thing to take a hands-off approach to the economy and player interactions, but if the system does not promote competition by allowing those with more game time to end up light years ahead of other players then what's the point? The game won't be successful without countless mercs and when things spiral out of control due to the unrestricted SP gain who will be around to play the game?