it's supposed to be 'hard' sci-fi. If there are lasers at all I will be sorely disappointed.
What?! No lasers at all? That's absurd. What have you against lasers?
We've already got the technology to shoot down missiles and stuff with lasers. If we're billions of years ahead in an alternate timeline in which we never stopped improving spaceflight, why wouldn't we have weaponized lasers?
You're not billions of years ahead. You're a handful of colonists who woke from cryogenic sleep billions of years after the rest of mankind has died off, with only the technological know-how they had when they went to sleep. In 1988. Even if they had never stopped improving spaceflight, they'd be at best a decade or so ahead of where we are right now.
Also, a beam of light that melts your enemy isn't nearly as cool as crashing a giant tungsten dart into him at a thousand kilometers a second. 
Ok, but from what I've heard it's an alternate timeline in which the space (and by extension, technology) race never slowed down, but sped up to the point where we actually had cryostasis capsules in 1988. Something which we don't have today. If we have that kind of tech, there's no reason to believe that we wouldn't have other kinds as well. We'll probably also have some form of FTL, unless you want a six-month real-time trip to Mars. Again, no reason to accept some technology and not others which we are actually capable of in real life.
There's also the fact that the machines have still been working after these billions of years (evidenced by the fact that humankind woke up at all), and it's not beyond the realm of possibility that they've been improving tech on their own.
And finally, giant darts may be cool, but they are speed and ammo-limited. Lasers would be far more accurate at range and wouldn't require the purchase and storage of ammunition.