Yes, I didn't mention this because you sacrifice so much spatial resolution and/or info doing this that it hardly matters, unless you believe in some very extreme and implausible forms of localization of function. (EDIT: I mean looking at a single slice seems to imply some commitment to localization assumptions; this isn't relevant for reducing spatial resolution.)

For readers who don't know, we can measure at a higher temporal resolution better if we use some tricks, and also massively sacrifice spatial resolution ("reduce volumes") and/or how much of the brain is scanned (look at single slices), but the spatial resolution in most fMRI given e.g. a 0.5 TR (2 images per second) is usually already quite poor (generally already getting difficult to clearly even make out gyri and basic brain anatomy: see for example Figures 7 and on here, noting the TRs in the captions: https://www.frontiersin.org/journals/neuroscience/articles/1...).

Still, it's a good point, and you're right of course newer and better scanners and techniques might improve things here on both fronts, but my understanding is that the magnetic field strengths needed to actually get the right combo of spatial and temporal resolution are, unfortunately, fatal, so we are really up against a physical/biological limit here.

And as you said, it isn't that useful anyway, because the BOLD response is already so slow, and obviously something just emerging from the sum of a massive amount of far more rapid electrochemical signaling that the fMRI just can't measure anyway.