There are some inconsistencies between FS1 and FS2. One of the biggest unresolved setups from FS2 is to actually see how the GTVA could destroy a shielded shivan capital ship as they advertise they can. It's quite disappointing in a way that there are no such shivan capital ships.
You could read this in some different ways. First, they streamlined the game and dropped the shield issue in favor of other more pertinent themes and story arcs, etc.
Second, within the world canon, you can easily imagine that the shivans did not have any other capital ship with shields other than the Lucifer type, and their mission in Capella was of a significantly different nature than the one in FS1, thus they used different types of ship. In this scenario, the Collossus was not designed to take out Sathanas-class destroyers. The Sathanas' biggest threat is its 4 beam cannons, which we can imagine to be more powerful than the Lucifer's. It is also really really big. You have to work through its hull a lot more than you would against a Lucifer, and if you spend too much time, its beams will rip you apart first (they are, by far, the most destructive weapons in all of FreeSpace canon).
Regarding how poorly it does against the Ravana class, I would suggest some solutions to the apparent inconsistency. First, the GTVA may have oversold its project. They may have been way optimistic in terms of what the Collossus was capable of doing. It may have been the case that, if faced against the Lucifer, it would do poorly against it. Second, it may just be that the Collossus was just too damaged from the beggining in its struggle against the Ravana.
In "the finest hour", the Collossus' engines are disabled. It cannot maneuver in a way that would take it out of the Beast's line of fire. In the meanwhile, the Beast shock jumps right next to the disabled Collossus and delivers its maximum beam power, while the Collossus' own beams are spread around its hull. That is to say, its strategic function of serving as a distraction (so that the Bastion could destroy the node) made it utterly vulnerable to shivan shock beam jumps.
So, the Collossus is physically damaged, rendering it unable to move, is in a completely disadvantageous tactical position, and is still able to destroy the Beast. I'd suggest it would be able to do the same against a Lucifer, given that the beams should be able to rip through its shields, canonically.