Number of non-doom weapons by kingdom (not necessarily released yet):
Summary
8 Ghulvania
9 Blackhawk
9 Sin of Maraj
9 Stormheim
10 Adana
10 Divinion Fields
10 Dragon's Claw
10 Glacial Peaks
10 Khetar
10 Mist of Scales
11 Blighted Lands
11 Bright Forest
11 Broken Spire
11 Forest of Thorns
11 Khaziel
11 Maugrim Woods
11 Merlantis
11 Pan's Vale
11 Pridelands
11 Shentang
11 Silverglade
11 Suncrest
11 Sword's Edge
11 Urskaya
11 Whitehelm
12 Drifting Sands
12 Grosh-Nak
12 Karakoth
12 Wild Plains
12 Zaejin
12 Zhul'Kari
13 Darkstone
13 Dhrak-Zum
13 Leonis Empire
371 total
You probably want to avoid maxing out 10-15 of those.
PL18 → 6 weapons maxed
PL20 → 8 weapons maxed
PL24 → 10 weapons maxed
PL26 → 12 weapons maxed
PL28 → 14 weapons maxed
Well, the books to upgrade a single kingdom to 20 cost >$500. They probably consider doom weapons to be in the same category of ‘FOMO cash premiums’ now.