But DJI don't collect your flight data, they don't get to see it unless you choose to upload it to their sensors.
If you ever have a warranty claim, they ask you to synch your data if you haven't already so they will have access to it.
But if you've ever seen what's recorded in flight data, it's pretty clear that it's got no espionage value to anyone anyway.
Sure, you absolutely have full control over the data collected as it stands, and can decline to send it to DJI if you wish. That doesn't mean there isn't some hidden functionality that would let DJI pull it remotely given the right trigger and a viable connection as the FUD-spreaders would like us to believe, but my view is that even if there is, SO WHAT? As you say, what it contains is of negligable importance for espionage (or any other practical use other than incident diagnostics, for that matter) in all but corner cases, unless they can also somehow grab the captured imagery. There are also third party tools online that can show you exactly what's in the information before you send it and, as I pointed out, if you are sufficiently paranoid you can absolutely prevent any of that data from being sent to China.
A corner case might be surveying within sensitive areas. If a foreign agency were to detect a drone flying a grid in an area of interest (on a military base say), then that might be enough of a trigger to prompt a futher investigation by other means to see what was going on - an "interesting" new construction, perhaps? Or, if you see a drone operating on a military base or training ground, then it suddenly pops in a conflict zone. Of course, that *still* requires the initial telemetry to be captured, transmitted and analysed, which doesn't seem to be happening either, let alone any of the bulk downloads of the user captured data that are being implied.
Users would notice the big data transfers if their images or videos were sent to DJI.
I explained here why the idea that DJI or China collects and looks at your images makes no sense.
https://www.flightglobal.com/military-uavs/pentagon-approves-five-us-drone-makers-ahead-of-likely-ban-on-chinas-dji/139864.article
mavicpilots.com
Yes, if they were looking for it, that would absolutely be noticeable if done in bulk; a trickle of telemetry data maybe not so noticeable for a general user unless they had a *really* expensive data plan or got stung on roaming rates while overseas though. However, people with a clue and interest in such things also deliberately go looking for this kind of stuff (Kevin Finisterre was mentioned above, for instance) and would be screaming blue murder if they had any evidence it was going on even if just for the street cred it would bring in the current political climate. Instead: *crickets* and *tumbleweed*. Lack of evidence doesn't mean it isn't happening, but DJI are being incredibly subtle about it if it is.
It's exactly the same as with Huawei - lots of claims, over many years, absolutely no evidence (or even evidence that evidence exists) made public. OK, it's possible that revealling that information publically might potentially compromise an intelligence asset, but the US has approached multiple countries that it routinely shares classified intel with over Huawei and - AFIAK - while a few have banned or restricted use of Huawei equipment, NONE have come out and said anything along the lines of
"we've reviewed the evidence provided by the US, and have decided to ban Huawei from our telecoms networks as a result".
Is there a risk? Yes, sure. Is it large enough that people need to worry about? Maybe, but only if you're in one of those extreme corner cases, and even then there's a good chance it can be managed. Ulimately, this is about almost entirely about money and trade deals, and absolutely zip to do with national security.