Burning your Mythic abilities and Domains on a few pet levels is the opposite of overpowered, massively or otherwise. Classes without pet levels are designed to be played without pets. There aren't that many pet items to go around, nor are there the buffs that make pets viable if you want to have functional characters. You're just running in circles.
Last several pages it is you who is running in circles with your domains obsession.
I had run domain-spamming Sosiel couple of times and my experience was thoroughly meh.
In low-tier fights domains are not worth the clicks wasted on them because everything is zerg-rushed in RTwP.
In mid-tier fights in TB all high performers like archers and ray-casters, who can potentially profit from his domain buffs, are way way before him in initiative order and delaying their turn will only give the enemy chance to fuck your party. And Sosiel's initiative is both horrendous and almost unsalvageable at the same time (Lann Inqusitor would do much better). So when he finally gets his precious clicks all priority targets are already shot/CCed/burnt to crisp.
And in select uber important fights where, for example, Community Domain, would be priceless (Nocticula, Baphomet) you can't even put it up before the fight due to shitton of scripted events.
Of course, they are still very useful in the rare fights where you can prepare beforehand and that last more than 1-2 rounds, like Playful Darkness and maybe Pathetic Quasit, but those are extremely few and far between for my Hard/Unfair parties. So choosing between Scald and Cleric as support luggage for my Unfair run I would take Scald (with his up to +14 AB buff and party-wide pounce) ten times out of ten.