I think you are right and are doing exactly what I would do. No, not necessary to inhale for 30 seconds.

I have done "Power of 10" which is a slow rep protocol. Also I did 2 years of a 3 year degree in Phys Ed, so i did the weight training part, metabolism, and physiology. Some thoughts, in no particular order:

Sometimes body builders of the old school, used the inhale as structural strength. That is, the air filling the inside, plus hardening the musceles around your core, built a tower of strength that assisted in some lifts in some conditions. Perhaps that's where they get the "inhale on lift" meme, don't know.

- When you are holding your breath you end up relying on the air column and paradoxically not using muscles as much. Beware the held breath. But a pause between inhale and exhale is different - the held breath has a closed throat.

- how much you can inhale, how slowly, can be trained. if you want to do more than now it's possible to increase your rib cage capacity and all that but not really necessary. Unless you want to train to take bigger breaths and hold them.

- Body builders in the past didn't go in much for super slow protocol so the breathing guidance is from different set/rep/tempo schemes.