I definitely suspected this. 7-OH levels from mitragynine conversion are rate limited, maybe that's why withdrawal onset seems extremely variable to me based on dose.
With high levels of pure 7-OH introduced, this would lead to much much higher levels of mitragynine pseudoindoxil, which is apparently a full mu agonist compared to a partial agonist. I suspect pseudoindoxil does cause significant respiratory depression. The nods from this stuff are much closer to real opioids, I can definitely feel respiratory depression too. Luckily I have not felt any need to take more than 15mg every 5-6 hours, probably because there isn't a reinforcing mental euphoria to it. "Less is more" seems to also apply to 7-OH somewhat.
"Inhibition of CYP3A reduced mitragynine-induced respiratory depression and anti-nociception without affecting the effects of 7-OH mitragynine" - This is fairly curious. If 3a4 is the only pathway for mitragynine -> 7-OH in vivo, why wouldn't inhibition lead to lower levels of conversion? Also, this implies there is some other respiratory depressant in kratom other than mitragynine or 7-OH