Raw, the Novalith isn't OP by any means. In fact, it too can be countered, though in the case of the Novalith, by Auxiliary Government or the racial equivalent. Now, you can say, "But it's so expensive to do that!" to which I respond saying that there are economic possibilities with starbases. All races have trade ports plus something else. TEC actually has two levels of trade ports, Advent has culture, and Vasari have Colony Pods. Oh, and Planetary Shields, Hardened Cities, and Fortification Specialists will also all deal with the damage to the planet.
The ability to nuke planets actually has almost nothing to do with its power. The real reason why its useful at all is it drastically reduces the income from that planet for an extended period (both trade and tax).
Novas are strategic weapons with a small tactical element to them, yet people never note the strategic parts while only noting and claiming the tactical component is OP even though its not. Beyond that, the devs added a superweapon cap just because some SP couldn't defend themselves against it.
As for the DE, it is widely agreed upon as the weakest superweapon because culture centers counter it so easily. That said, you have to consider that it helps the Advent fight in their culture and also gives a 25% boost to damage for all friendly ships in the gravity well. For the AL in particular, this makes them quite powerful and much more difficult to kill.
That said, its still kinda UP, so people have made suggestions for things like making it capture the culture centers in the enemy well. There was actually a lot of discussion on this before the Vasari were added (and with them, a slew of significantly more problematic balance issues).
If you want to talk about the most powerful superweapon, there's only one option left, the Kostura Cannon. Sure, the disable isn't as useful against economies as the Novalith, but it is the most tactical of the superweapons and is far more powerful in a game, particularly when used by the VR or when playing with capital victory. You see, beyond the disable, it does something else: it creates a phase node. That means that you can jump your entire fleet to that planet and wipe it and surrounding rear-world eco planets out with minimal resistance.
OP, the TL aren't the strongest race by any means. In fact, they're one of the weaker ones and seldom played on MP because the Novalith isn't all it's cracked up to be, particularly since the superweapon cap. The TL turtle and build superweapons to soften their enemies. Against a player who knows how to defend against it (just upgrade your planets' health for starters or build starbases), it really isn't hard to take the blows. You just have to know how to take them.