It's viable, but not all that great. You can still get some pretty potent burst going, but it can be tricky to pull off sometimes (which isn't actually any different in Summerset than it used to be). Some players are very good at avoiding Deep Fissure through movement and/or properly timed CC, and super-speeded Stam builds that move around right on top of you are the worst. It's also pretty annoying that Destructive Clench with a Flame Staff may sometimes knock an enemy in an unexpected direction, and actually cause them to avoid your shalks through no action of their own.

Being spam rooted really gimps a Mag Warden's damage output as well, obviously, and unlike melee builds you generally can't afford to do a bunch of dodge rolling, or get root break/immunity through "normal" gameplay methods. It's possible to use a non-staff 2h weapon with Forward Momentum, but that will eat into your precious stamina pool, and take up bar space that's pretty hard to find.

In my view, a Magicka Warden really has to build "tanky," though not necessarily using one of those HP-focused builds. Those setups might be decent utility and AOE pressure if you're running in a premade group, but it honestly seems quite bad for solo queueing (I've never run it myself, but have watched/encountered other people using that type of setup). Your damage can look good on the scoreboard, but don't expect to land many kills solo if you come up against anyone halfway decent.

My own "tankiness," to the extent that it can exist in the current patch, comes from wearing Pirate Skeleton with 5 light, 2 heavy (Necropotence and Shacklebreaker with Triune jewelry), keeping Ice Fortress up, and spamming Harness Magicka and Healing Ward when under pressure, along with a Destructive Clench stun if able. Besides that, you'll obviously want to line-of-sight enemies as much as possible, and sneak in some meditating whenever you can. The Major Protection and health and magicka returns are nice, but keeping your stamina as high as possible is really vital. A large percentage of my deaths happen because I ran out of stamina and couldn't break free.

It's also possible to escape with Nature's Embrace (the vine pull/heal), which can be a real lifesaver sometimes, but your teammates often won't be cooperating with that skill when solo queueing. Usually, you're going to be tanking quite a lot of damage because Major Expedition isn't going to help you enough when you're snared (and you will be snared...a lot). Cleansing debuffs and DOTs with the Blue Betty is fantastic, but not always an option, depending on the number of debuffs and amount of incoming damage.