I agree that chaplains need changes/buffs, but I don't think converting them into loyalist dark apostles is the right way to do.
I find that their abilities are, at the very core, correct: improves morale and everyone fight better around them. But I think there is a double issue:
One is about rerolls: marines usually hit at 3+ both in shooting phase and fight phase, that makes rerolling 1s a very powerful buff, because you only miss at 2s. And there are other units which, without being that good at giving rerolls around them, do enough to displace chaplains, for example, captains and other equivalent units which also give rerolls to both the shooting and fight phase.
Second one revolves around the leadership bubble: while on the paper is good, on the table is not that good because marines are played in small/medium size units and have good base leadership stat. That alone, with the current morale rules, decreases a lot the strength of this ability. And I believe that against -ld bubbles, the leadership bubble doesn't prevent to falling into low ld (also, there are too few units across the 40k armies that do this). Add ATSKNF into this redundant train, being baseline for every marine, into the mix and you get an ability that most of games you don't even use once.
Given that the majority of SM armies leans more towards shooting rather than melee doesn't help either, talking about the fight phase rerolls.
How to fix this? Tough call. Either you make chaplains true and glorious monsters at CC, or you nerf reroll abilities of almost everything while buffing his ld bubble to the levels of auto pass morale checks.
Sadly, I can't see any fix for our chaplains in the short time. Maybe with a new edition...