"EQ to the level of the inferior sub" may not be exactly correct. Rather, if one sub has significantly different (i.e. inferior) performance, the combined performance of the two subs could be degraded. This is a complex question that depends on a number of factors, including placement of the two subs. That's why the recommendation is to always have matching subs.
I looked into those features before buying my Onkyo 818 which has XT32 but no Sub EQ HT. Here's my understanding:
XT32 (with or without Sub EQ) will eq the combined response of the subs. It doesn't know if one sub is inferior to the other since it measures them together. Yes, Sub EQ sets individual distance and phase for each sub; it then applies a single eq filter to both subs (same thing XT32 without Sb EQ does). In other words, XT32 will always apply a single filter to all subs based on the combined response. If you have 2 subs, Sub HT will first set distance and phase for each sub before applying that single filter. If you have 1 sub, Sub EQ HT provides no benefit. If you have more than 2 subs, it may not provide a benefit either.
If you have more than two subs, you still get the benefit of SubEQ HT. However, you should pay close attention to the placement of the subs. For example, I have four subs, and each sub "pair" is equidistant from the MLP on a separate sub channel. Each sub in a "pair" is gain-matched with the other sub. This way, SubEQ HT correctly sets the distance and trim for each pair.