Totally agree that the current situation is imbalanced and doesn't create fair gameplay. In my opinion it's ok for the death rate to be this strong, but they shouldn't ALWAYS be this strong. I agree with you that the upgrades for the weapon are the problem. The base stats are fantastic, and the upgrades are useless. In practice this means that EVERY celestial death ray you face is absolutely deadly, and if you come across 2+ at once (fairly common), you are gonna get wrecked. If the weapon were balanced so that it had to be upgraded carefully in order to be effective, the average threat a random death ray presents would be lessened, but the player could still use them as a super weapon if they really invest into the upgrades.
I've struggled with celestial death days quite a bit too, as you said they are only rivaled by unknown laser cannons. The celestial death ray does too much hull damage to defend against. However, if you have a strong shield buffer and decent shield repair, you can prevent it from ever getting to your hull. This is the strategy I have had the most luck with. However, the celestials are unique compared to most other races. Their weapons are generally very good at stripping away shields, and their death rays are one of the most destructive hull weapons in the game. This makes them imbalanced and extremely difficult to defeat. Most other races only do one kind of damage well(trolgar using projectile cannons to damage hull), or if they can do both they are only effective at certain ranges (wanderer flak cannons for example). Celestials break this trend and leaves no real effective counter against them.
The other problem with death rays is that they are, in a sense, the "perfect" weapon. Their combination of long range, accuracy, and high damage, makes most other weapons obsolete. There has to be a trade off, right now there isn't.
