I absolutely intended for this suggestion to be something for the distant future, not something to be implemented soon.
I think Story Mode not having pet buffs is a great idea - I feel that Story Mode serves more as a tutorial and introduction to the game than the core of the intended experience (spoken with the assumption that the rest of the major planned features make it into the game in the future lol)
The Pet System would be something more intended to provide some extra buffs for Endless Mode; to extend gameplay a bit and let you push a little farther, and maybe a little faster. (Some pets might add enemy spawn speed or reduce enemy HP growth by a small chunk; or aught similar)
By all means, please focus on the other major features. I had a thought, wanted to share and get you to noise about it if you were interested at all - and it looks like it’s a hit. I’d much rather see Endless mode than the Pet system lol.
Thanks for adding it to the list, and thanks for the information.