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So, obviously the most popular - Blaster mastery build with azerite trait stacking. The main question - is it worth to use 370 ilvl blaster mastery gear over 385 uldir/random-azerites pieces?
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The last one i want you to share you thought about stat distribution and simulations (raidbots/askmrrobot), should i believe in their result and numbers as, for example, BM build is like walking on the 0.1-0.2 second edge of keeping the buff up, so i am not sure that the numbers are accurate in simulations.

Pyroclasm is viable but i think it does considerably less damage then blaster master builds.
Ive been playing pyroclasm since the start of Uldir and at the start of this tier was able to get good logs with it.
Compared to my guildies it was bad though... but since fire received 2 flat buffs the DPS was similar to most other guildies on other classes.
Ive been middle-of-the-pack DPS in our guild which is now 8/8 HC - 3/8 mythic.

But since more and more fire mages play blaster master, my logs have been dropping considerably. If you want to compete with other firemages for good logs, there is only one way to go it seems... blaster master.

Pyroclasm can still do good dps, (good enough to meet raid-boss requirements) i would define this as viable
But you won't out-dps most other, similarily skilled dps on other classes.

The upside of pyroclasm is that it is pretty easy to get in to. it can be played with IF or Rune of Power (with RoP performing slightly better in raid, and quite a bit better in m+).

Statwise pyroclasm is most compatible with Crit and haste, but versatility isnt far behind. Mastery probably isnt the best pick for raiding, especially if you have blastermaster traits on gear (that devaluates mastery a lot).
Ive raided uldir with crit as highest stat, and haste as highest stat, and for me personally getting crit highest for the Array buff got me the best results.

TLDR:

Pyroclasm is fine (for meeting minimal dps requirments of uldir bosses) if your guild accepts playing sub-optimal builds. You won't get great logs, and wont out-dps similarily skilled people on most other dps classes. Blaster master DPS potential is much higher.