Both sides' tactics in this mission leave a lot to be desired.
The GTVA don't seem to have anticipated that after the Shivans send a Cain, then Lilith, then a Moloch, then a Ravana, one of the 80+ juggernauts they have in system might hop over.
I don't see why the Colossus was there at all. If the aim was to draw bombers away from the Bastion surely you want things that bombers can be useful against - send the Aquitaine, the Memphis, maybe even just the few cruisers they did send. In fact scatter lots of little battlegroups around harassing Shivan positions. By putting the Colossus there you're practically begging them send a Sathanas.
Then of course there's the real problem with the GTVA strategy - why are they sending the Bastion through Capella, a contested system where the Shivans hold a massive advantage? Surely it makes more sense to send the Bastion through GTVA space to Epsilon Pegasi the long way round. It's 5 jumps. I know they want to get the job done quickly, but the risk if they don't make it is insanely high.
The Shivans on the other hand, send several ships to their deaths facing overwhelming firepower when they've got 80+ juggernauts in system. The Beast obviously stands no chance against the Colossus, it's just cannon fodder.
Narratively I don't think it works that well either, the purpose of the sacrifice isn't well communicated, it's clearly supposed to be this heroic sacrifice to buy the Bastion time, but it's never really explained how they're helping the Bastion.
If I were rewriting it I'd have the Colossus be in one of those evacuation missions towards the end of the game. It's hanging around at the jump node deploying fighters. A Ravana comes in and starts decimating the convoy, the Colossus is ordered to jump out of system, Command notes that there are 80 juggernauts in system, Shivan activity is rising. It refuses and turns back to attack the Ravana. It's victorious, the survivors are leaving, but as the Ravana's going down, three juggernauts warp in and obliterate it. At least then it's actually obvious what it's dying for.