I think the focused training on grip fighting/pummeling, positioning, and finishing mechanics can make a lot of sense, assuming there is both dedicated tachiai practice as well as full match practice elsewhere. This approach is also likely to limit some keiko wear and tear.
This is effectively what's called situational drilling or sparring in wrestling or BJJ and allows one to drill specific techniques against full resistance in a deliberate fashion. That is, it's all well and good that you learned an uwatenage, but if you are just doing full match sparring from tachiai all the time you won't be able to get in enough repetitions of the technique to make it effective.
So, drill the finishing technique, then zoom out and drill a gripping sequence to the finishing technique, and then zoom out again to tachiai to gripping to technique. As a pedagogical system, it produces very high level grapplers, so long as all parts are worked on appropriately.
Time will tell, but for the moment I doubt the rikishi are getting zero tachiai practice, and if that becomes a hole in their game it can then become the focus of drilling as they go.