It is viable in the sense that you can be successful with justicar, it isn't some combo of 3 trees which have no synergy, but I wouldn't call it optimal or meta at all.
There's a few kind of cheesy applications of justicar, for example like imprisoning yourself and then spamming mend with pain harvest active.
To put it kinda simply, other classes just do things better.
Unfortunately justicar lacks mobility outside of mana barrier and shadowstep, so you'll have to rely on gliders or mounts a lot.
For 'frontline' style classes, people nowadays typically opt to take auramancy which can provide several CC immunities/breaks (courageous/shrug), mobility (teleport, comets boon), and survivability (thwart, wings, health lift, conversion shield).
I'd recommend switching it up a little and trying either edgewalker (vit/aura/occ) or heirophant (vit/aura/witch), both could be good options for you.