I don’t think anyone addressed this specifically: The driver and spring are certainly 100% capable of 2.8 amps. The problem is that your LED has a high Vf needed for that current (out of the driver’s control!) and your battery is not providing a voltage significantly higher than the Vf needed under load. This is a common problem and has nothing to do with the driver. Resistance mods reduce losses to try and make up for the problem. Reducing losses is always a good thing, but you could also attack the problem by choosing an emitter with a lower Vf (this will be difficult for you to do) or a battery with a higher voltage under load (this is easy to do!).
Look here to learn the shape of the curve which determines what voltage is required for different currents. Each generation, series, and individual emitter is somewhat different but this will teach you a little:
djozz - Crash-testing a XM-L2 and a XP-G2 on copper Sinkpads [Post #51]
Look here to learn about different batteries and how their voltage sags under load:
HKJ - Battery test 18650, comparator