It is indeed a strong nerf to Hallowed which was intentional in order to bring it more in-line with the proposed Living Dead and Superbolide, just like raising Holmgang's recast by 120s to 300s (almost double) is a strong nerf to Holmgang and for the same reason. Both Hallowed and Holmgang are relatively too strong and really do need to be nerfed.
Basically with the changes I proposed Hallowed is entirely proactive, where all preparations such as healing are front loaded. You want the PLD's HP to be as topped off as possible before they use it. This introduces an element of skill and different considerations to it's usage. If properly executed it is little different than the current version, you just heal right before as opposed to during. Conceptually it just pauses the state of the PLD's HP for 8s, nothing in and nothing out. The longer recast compared to the others, which is actually the same as it currently is and less of a difference than the current spread of recast times, is because Hallowed would be the only invulnerability that has the chance under the right circumstances to completely negate much if any need for healing to compensate for it's usage.
That then gives Superbolide it's own reasonable niche. It stops damage entirely like Hallowed but reduces the GNB's HP to 1 which means it will likely remove health that then needs to be compensated for and since you can't leave the GNB at 1 HP it forces the healer to have to heal the GNB up. The aspects of it likely forcing both lost HP and required healer intervention is why it is where it is recast and balancewise.
Living Dead basically acts just like Superbolide but puts all the responsibility of healing on the DRK themselves since it stops external heals but empowers self-healing. The pros for this versus Superbolide is that it completely negates healer interaction during it's duration but it's cons are that it is inherently riskier since the DRK could bungle their self-healing and that they won't be able to top themselves off so the healer will likely have to be ready to react with a quick heal once LD wears off. The inherent risk seems like a fair trade off for potentially less needed external heals and that's why I put it on the same recast as Superbolide.
Holmgang gets to keep the lowest recast because while it stops death, the WAR still takes damage for the duration so any incremental healing or self-healing still gets drained while it is active leading it to potentially requiring the greatest amount of external healing. Also keep in mind that there is a huge difference between a 300s recast and a 180s recast, so even with having the lowest recast of the bunch it would likely only get one extra usage in most fights if any at all and we wouldn't be seeing the ridiculous usage disparity we have now.
Basically the recasts were set based on potential healing required to get back to where the tank was when they used it, with a general shift towards longer recasts overall.
Is what I came up with or expanded on perfect? Not by any means, I pretty much came up with it stream-of-consciousness but all in all it's actually not too bad, well unless you are really really opposed to any form of nerf to Hallowed or Holmgang at which point we will just have to agree to disagree.