I play pretty much only in CP (Cyro, IC, no BGs) and I don't play vamps for role-playing reasons. With those constraints out of the way, I have never felt that heavy was meta for magplar. You lose too much damage and I feel Malacath is overrated in general, at least in CP. I have not tried it on magplar, though, mainly because I prefer Wild Hunt over everything on every build. That isn't purely defensive by the way, as it can also help you stay in range of your target while you're jabbing.

The change back from 60% healing reduction to 55% in PvP sounds like nothing, but I think healing changes disproportionately affect templars and mine feels quite solid again. Furthermore I tried various tanky options in the past, such as Pirate Skeleton, Pariah, Armor Master and Cyrodiil's Light - not all at the same time of course. For me those options all pale compared to what I've worn over the past two weeks, something I threw together in exasperation, which is:

5x Eternal Vigor
5x Amber Plasm
1x Skoria (pen)
1x Wild Hunt
Atro Mundus
Stamina Rune
Sugar Skulls
All prismatic glyphs

Bear in mind I don't use Mist Form and that I highly value speed, hence my preference for that mythic. The stam sustain is way over the top in this build with 1.3K stam regen plus the rune and 17K stamina, but boy does it play well. Far superior, defensively, to any tanky set up you could wear, IMO.

The problem has been lacklustre damage, which became especially obvious when duelling a friend on his stamcro, although the magplar was defensively very sound in the duel too. I'm about to tune the build as follows:

https://en.uesp.net/wiki/Special:EsoBuildData?id=293968

E.g. Amber Plasm + War Maiden front bar and a Master's 1H+S back bar. This brings us to one of the recent changes: Pierce Armor now grants Major AND Minor Breach, bringing total penetration for the build to 18K. You also get another heal and more resistances from the Master's set.

In terms of a front bar set, Stuhn pairs with Toppling Charge and would stack another 5K pen, but with this much already I thought it was questionable in this particular build. Overwhelming Surge is IMO good on magplar, not least for the NB detection. There's probably any number of other damage sets that would work, but note how War Maiden was buffed to 600 spell damage on magic damage skills, hence I'm currently wearing that.

Skill layout is up to you. My build is AOE centric. I personally wouldn't change the back bar, but the front bar is totally flexible, with the obvious missing skill being Purifying Light in my current build.