That is not what anyone is saying at all. I'm the one saying that. Everyone is just saying "There is only 1 Force resistant monster".
Congrats to you all for reading. That doesn't mean Force is the ultimate damage type. Everyone is just repeating numbers, and I've run several campaigns where Fire resistance didn't exist.
Yes there are a lot of creatures that resist fire, doesn't mean they'll always be used. Hell, with how worthless Poison damage is it's a wonder it even has spells. Only 1 Dragonborn option even uses the damage type. There's such a high chance for a creature to be resistant or immune to poison the fact the spells aren't that strong would suggest the devs don't look at damage type when balancing spells. Wouldn't it make sense for spells of a weaker damage type to do more damage to compensate?
But then the spells would be a go to for creatures that don't resist it. Force has very few spells that use it. Magic Missile is the weakest spell in the game. It can auto hit yes, but it maxes out at 11d4+11 if all hit the same target. If it was fire or thunder or even poison it would do the same amount of damage.
Fire spells are abundant and are often the stronger damage spells. And it's not even the weakest type. Not to mention Poison spells are on the weaker side for their level because they impart the Poisoned condition. Which means a huge portion of monsters will be unaffected by the condition. Con is a strong save for a lot of monsters, and poison resistance is always paired with advantage to saves against the said condition.
Force has 1 resistant creature, Fire has several vulnerable creatures, and Poison is one of the worst options for damage a Player could ever choose.
If people were saying anything close to what I have, that campaigns can change the perceived balance of damage, I wouldn't be downvoted. Everyone is just saying Force is better because only 1 creature resists it. There is a Magic Item of uncommon rarity that can grant resistance to the God of Damage Types. By the DMG that level of rarity is suitable for tier 1 play. That means any creature able to attune to it can become resistant to Force damage. Does that mean anything? Is Force still powerful when the amount of creatures that resist it can be raised from 1 creature to 100?
A creature having a Brooch of Shielding is just as likely as it having Fire Resistance. In fact the Brooch is more common than a Ring of Resistance. So it's easier to gain Force resistance than Fire Resistance. This is all within the rules, as nothing says magic items can't be used by enemies.