Your point about segmentation being the key to interpreting that 38.5% read rate is exactly right. In my own tracking, a segmented post-purchase flow consistently hits the upper end of your 45-60% range, while a generic newsletter blast sits at the lower end of that 15-25% promotional bracket. Treating them as a single metric is useless for optimization.
The 95.6% deliverability as a diagnostic floor is a solid use of the report. I'd add one caveat: teams should also track their own *inbox placement rate* separately from this blended deliverability number. A campaign can technically be delivered (not bounced) but land in spam, which that 95.6% figure doesn't capture. That's where your point about authentication becomes critical for the final mile beyond just getting past the gateway.