Dropping my 2 cents here.

I actually contacted Ola just yesterday I think 🙂 ... for a very similar question (what a coincidence)

I've implemented his solution but found that some reports were running slow after our daily or weekly data upload. So I was told that by default, Ola's solution does not update statistics, the ReIndex job I mean. I added that option as part of Saturday's weekly plan.

Now, by experience, and like you said, updating statistics should be done after major data insertions, so the queries will have fresh statistics and execution plans will be based on that, minimizing the chance of picking the wrong execution plan or Index.

So ... my advice ... validate your data upload schedule. You can update statistics as part of your store procedure's logic or, you can run a daily job just after that data insertion.