I will give an example.
Sisters Repentia cost 17 points, has an Eviscerator, FNP, Rage, Fleet, Fearless, Acts of Faith and Shield of Faith. They have the Spirit of the Martyr AoF which allows a model killed in assault to still be able to make a single attack...
My suggestions were simple. 14-15pts each, Holy Rage, Fleet, Fearless, Adepta Sororitas (allowed to use Acts of Faith). Spirit of the Martyr as a unit special rule so that they could use it even if killed in your opponents turn and without having to make a test to see if you could do it. The option to take a transport but once you left it you may not embark on another one for any reason.
There's no question that the WD codex was a hastily thrown together piece that messed up a lot of things, but it isn't terrible enough to warrant a 50 page rebuttal either. I'm not certain most of the net wishlists are that desirable either, or any more play tested.
Taking the example here, sisters repentia are one of the main components of my army, and I rely on them to accomplish a lot. I would love a dedicated transport so I don't have to load them up in the backfield on turn one, I would love for their AoF to be automatic, I like holy rage but I see how it complicates things needlessly.
But I look at your proposed changes, and I don't see any kind of save. With 6++ and feel no pain, I can count on my repentia winning the majority of combats they get into, and I can generally count on them hitting at least two more units, albeit with diminishing returns and numbers. They get far more done than my death cultists, certainly. Without these saves, I doubt they would win even their first combat, and getting off a few spirit of the martyr hits doesn't even begin to cover the loss of utility. They would never survive a counter charge. I can't see taking that unit, even with the point drop.
On the other hand, if they have some kind of 4++ save (like they used to have) AND the changes you have made, you would be a fool not to take them at that price. Losing the 6++ on top of the 4+ would hurt a bit, but losing the vulnerability to instant death is more than worth it. I'd love that unit, but people would call cheese, and rightly so. Repentia have a larger threat range, are more durable, and can kill a much wider range of targets than DCA. At 14 points, improved abilities and a transport, they would be a steal.
Your changes either take away all their weaknesses, or turn them into a suicide unit that will generally die *before* getting off their suicide attacks. I'm not sure I think either direction is an appropriate way to go - but if you have to convince games Workshop of one, I suppose I would prefer the former
Honestly, the only fix I feel repentia need is a dedicated transport, and maybe a way for the mistress to override rage for a turn when you really need to nudge them another direction.