But the Murders do not have the capability to deploy fighters themselves, and if they have separate carrier support, so too can the IN have carrier support and/or screening waves of torps.
AAF does not reduce the effectiveness of IN prow weaponry, which assuming a start from within 60cm (fired on by Murders), allows them to close an average 34cm to well within shotgun range with no chance of intercept. Even assuming that one of the IN ships is forced to brace/cannot get into range/is intercepted, the two other ships by themselves are rolling 10D6 after turrets against 5+ ignoring shields and hitting subsequent targets vs the Murders' 12D6eq against 4+. By themselves those 2 ships have nearly equalled the Murder's damage past shields.
Following that, the range is already 30cm, and due to the angles involved it will inevitably get closer. At such close range the murders will be outgunned and outmanoeuvred and expose their vulnerable prow to IN broadsides. The IN holds all the advantages and none of the weaknesses now.
Contrast the Carnage. An abeam profile allows it to:
Follow an oblique withdrawal, slowing the enemy rate of advance.
Lead the enemy fleet, thus slowing its advance.
Less vulnerable to torpedoes fired from beyond shotgun range.
In addition, its ability to focus its firepower means that unlike the murder, it will outgun the closing imperials until they break the line - further slowing the moment when the advantage is given up.
So the Murder gains no advantage against imperials by closing, and almost actively seeks to lose its natural advantages in doing so. The Carnage makes best use of Chaos's natural advantages and hangs on to them much longer.
I'm not saying the murder is useless - it's cheap and has reasonable range. If it hangs back in an abeam profile it has a reasonable chance of converting tis range advantage into a victory over its IN counterparts. But using the prow weaponry is asking for trouble, and if you're going to hang back the Carnage is better by miles.
And that's just against IN! Against Orks you want to be close even less than against IN. Against Eldar those lances are useless, whilst the Carnage is a born eldar-killer. Against Ad Mech, Carnage or Slaughter Chaos you are saying "yes I DO want FP16 across my 5+ prow!" whilst even against Murder-Chaos you'd be better off abeam than facing down long range WBs with your prow. Only against Necrons do long range prow lances come in useful, and you're STILL exposing your prow to Lightning Arcs.