I see a lot of people saying "I bought a 50 bundle I should've gotten a diamond"

Not necessarily, pack odds are all about probability at random, not per every 50 packs. So each pack has its own odds.

100% of the time you will pull at least a bronze

Diamonds are 1 in 50, meaning you have a 2% chance of pulling a diamond on any given pack. I would assume that within that 2% there is an undisclosed probability on low Diamonds 85-89 compared to high diamonds 90+ so the odds of pulling a Trout are more likely to be 1 in 25 or worse out of that 2%

It's all math, and each pack is random regardless if you buy 1 or 1000, and the house always wins.