Hey John,
I'm not going to go too indepth into BG mechanics, but suffice it to say there's a lot of skill and knowledge required to know how to play them properly and actually make units off them. It would make no sense for Plarium to give players a way to just 'make units' out of thin air.
That said - the knowledge I have of old BGs, when they were still being found out, tells me that with all those units combined, you maxed about 1.7 'banks' for a level 100 bg, so those units doesn't cover 2 full banks at level 100 (this could be inaccurate, you'd need someone who plays bgs to confirm). However; judging by the fact you were throwing bestiary and occult units at BGs like that, makes me thing any number of things happened. First; you probably weren't aware that if your resources aren't maxed, battlegrounds will reward resources instead of units. Second, the battlegrounds take a tax regardless of what you win, so you will never recover more than you throw in, so you won't get 1 dragon back for every 1 dragon you use, which is why all the advice I've ever seen is use infantry and cavalry and 'upgrade' them.
There's more factors, but I'm pretty sure this isn't a bug. You probably just need to spend a bit of time reading up on how battlegrounds work
https://legacy-stormfall.blogspot.com/p/battle.html
https://plarium.com/forum/en/stormfall-age-of-war/53_game-tutorials/74850_my-personal-guide-for-battlegrounds/
https://stormfallguide.blogspot.com/p/battlegrounds-guide-maximising-rewards.html
Here's some links, they will hopefully give you a better understanding of some of the mechanics and how to start building your own strategies for BGs to maximise what you get