Heir Apparent was already a cool Exotic in Destiny 2 but the Catalyst makes it a force to be reckoned with, both in PvE and PvP.
Heir Apparent protects Guardians with an Arc Shield as it spins up and while it makes them chunky, their Crucible opponents can easily one-shot them with the right equipment due to the slowdown the weapon imposes. In this case, it would be an Arc Sniper Rifle that turns the shield against the Guardian.
The Catalyst takes away that threat in a sense. When applied, the upgrade will make the shield extremely resistant to damage, r educing damage taken by 75 per cent from all sources except Arc, which is diminished by just 62 per cent .
If you are not yet sure why this is so significant in the Crucible, it's because Behemoths were nerfed in part due to being too tanky while under the effects of their Super. Namely, it used to reduce damage taken by 60 per cent, which is less than what Heir Apparent's shield absorbs, even when countered by Arc damage.
That said, the weapon slows Guardians down when they are firing so they can forget all about mobility, especially the dreams of Behemoth-like zipping across the map.
Still, the weapon will take some serious firepower from the enemy team and one lone Guardian should theoretically be able to sow chaos in a group of opponents. Until they get frozen and instantly popped, that is.