The new pantheon on paper is approximately equal to Stars and Sky for mine/quarry tundra monopolies. What I mean is it gives an effective +1 yield on tundra tiles and then +2 yields on mines/quarries, for +3 total, just like Stars and Sky. But then the pantheon is better if
(a) you get snow resources (rare on this map type it turns out, but they are always mine/quarry resources, so you get +6 yields)
(b) you work tundra tiles without resources. n.b. tundra hills with caravansary are already superior to grassland and plains hills, this makes them another yield on top of that (effective 4 yield base)
(c) you gain cities off tundra with mine and quarry resources, which will basically always happen (here the capital already has a plains Amber tile)
Now, given its the UA, could it be a bit more powerful? Perhaps. Maybe! Possible options
+3/+3 yields per 4 tiles (
50% more)
+4/+4 yields per 6 tiles (
33% more)
I think +4 yields per 2 tiles, i.e. +2 yields per tile, is clearly too strong. Compare to Cernunnos that only gives that bonus to forest/jungle, and then also note that its plantations cannot overlap with that bonus, whereas tundra can have both mines and quarries. Of course, I am assuming that Cernunnos is balanced, whereas we could separately talk about that.
You have a slightly odd start because it looks like gems is your monopoly (good), but then you got a ton of furs in the second two cities (bad). So the tundra has been split between two monopolies. If you had more cities like Cardiff and Dublin then the Forest/Camp pantheon would probably be best. 5 deer and 3 (5 possible) fur is crazy! This choice is like how sometimes Goddess of the Hunt is better than Stars and Sky.
On the separate issue of Desert. I don't feel like there's any historical precedent for Celts living in the desert, and so it doesn't feel right to me. There is a God of Fire, but apparently he's like an Apollo character.
Finally I'd note that there are many options to pick that don't depend on your starting terrain, and so there's no pressing gameplay need to introduce a Desert one.