Actually not.
If we do Halo-style full-ship massive MAC (Mass Accelerator Cannons)-style weapons, then yeah, they can't track things. But the US Navy's present railgun prototype(s?) are small enough to be fit in a destroyer turret (Like a WWII guns-and-torpedoes destroyer) and still fire at extreme speeds in atmosphere. This makes it relatively easy for us to make one we can track missiles and shoot them down. (Large fractions of the speed of light? YES!) The problem in atmosphere is that the ammunition almost inevitably deforms on contact with the air. Deformed rails ARE an issue, but not after just a few shots. Plus, we're sci-fi. We can make non-deforming rails. Heck, it's probably possible, if we were to invent room-temperature superconductors and small fusion reactors or incredibly efficient batteries, to use a railgun system that never actually requires the projectile to touch the rails.
The basic premise of the railgun/coilgun/MAC gun is to invalidate all armor they might produce. If we make it, and then simply don't deploy it, we'll have a foolproof instantaneous one-turn hard counter to any armored vehicles they deploy. As well as a new toy for all our spacecraft. Speaking of spacecraft, for fun, I felt like writing something up:
Pillar-class Artillery Vessel
Using the hull of an Iliad-class, this interesting new development makes use of the full length of the hull, removing the missiles in favor of a huge railgun, based on the tech of Old Earth. The weapon stretches the length of the vessel, allowing for relatively gradual accelerations to high fractions of c. The weapon always points forwards, and all the thrusters are optimized for rapid turning over speed. The vessel fires a very large metallic rod, capable of punching through a planetary atmosphere to strike the ground with devastating force.
----This would be a good first development. A rod fired like that can reach speeds that result in impact detonations with strengths of more than 12 tons of TNT. Solves our artillery problems for all time, and as we upgrade sensors, we upgrade the ships to be capable of engaging hostile targets. Plus you can just have a few slabs of printed circuits sitting nearby to do all the firing calculations.