You misunderstood me. 40k weapons can reach out much farther the range where they can expect to get a positive sensor return from active sensors, so they don't run active scans to avoid giving thier position away. If Starfleet is running around blasting out sensor pings, the imperium will see them well ahead of time.
I'm not sure passive sensors would be able to work in this context. It works for a naval setting since submarines are constantly putting out signal/noise which is conducted through the medium they move through. So if you get a "ping" you can start stealthily searching for the source.
That's not really the case in space where not only would sound not travel but at the distances we're discussing even light is going to be considerably delayed and that's if its even detectable by the Imperials. So there's no real way to "see" the Federation starships.
Assuming the sensors beams used by the Federation are opaque to Imperial receivers that won't show them very much or, if ships are constantly sweeping beams back or forth, possibly anything at all with them detecting merely an amorphous, ever shifting wall of energy bombarding them.
And all of this presumes the Imperium actively uses/employs passive sensors to a meaningful degree. Consider the case of the Diasporex
. The Iron Hands spent nearly five months pursuing them around the Carollis system with it being a plot point the Diasporex were refueling from the system's star in order to resume their nomadic journey. Further we're told there are no other ships operating in the entire region beyond the Iron Hands and the Disaporex which is how they discovered the latter's existence when they detected Vox communication they couldn't account for.
Yet they could not find them, even through they want a confrontation and are actively pursuing an enemy who's primarily interested in running and hiding with the occasional ambush. Not even passively detecting the Diasporex's drive emissions which since they're constantly maneuvering around the system should paint a pretty trail.
Everyone else in 40k uses completely alien technology and most are able to innovate, and that doesn't stop the imperium.
Only the Tau would be comparable to the Federation. Necrons and Eldar have their ancient technology. Orks, while their creations are ramshackle, are all based on the Old One's knowledge and for the most part appear to rely more on raw brute force and numbers than technological innovation. Tyranids utilize biology rather than technology. Further nothing says the Imperium deals with any of these aliens with innovation of their own as opposed to raw, brute force.
Given that transporters have been jammed by mild amounts of radiation, thunderstorms, and all manner of other mundane phenomenon, trying use them to argue that the targeting sensors are infallible is a strange claim.
I wasn't making any argument in regards to infallibility in the section you quoted. I pointed out that if sensors have the precision/accuracy to beam a person while at warp there's no reason you couldn't use those sensors for targeting. As opposed to you attempting to use the Picard Maneuver as the benchmark of Starfleet targeting.
And the issue is that given we both have a very limited amount of knowledge for 40k naval engagements, arguing that since you don't know of something happening makes it impossible isn't very convincing.
It's a reasonable assumption based on what we know. While we should not misconstrue it for completeness on the subject of course but if both our knowledge of 40k naval engagements contains no reference to it that is a good sign it isn't a common element in their naval battles. Certainly it is no more of an assumption than yours that Starfleet can't detect a ship in the Warp or that Imperium ECM will meaningfully impair starfleet sensors.
Not to mention you've argued that Imperium sensor reach tops out at less than a light second. Even if they could automatically and instantly detect a warp-drive vessel at that range they'd have only some small infinitesimal fraction of a second to react. For a comparison, in the ambush with the Diasporex a cruiser captain considers torpedoes almost thirty seconds out "was practically guaranteed" to hit due such close range.
The point I'm making is that it decisively refutes the claim that Federation uber-sensors can axiomatically detect weak spots in absolutely anything, even alien technology that they're completely unfamiliar with. I'd normally consider such an absurdly broad claim to be a strawman, but it's *actually being argued* in this thread.
Nothing is perfect. However the example tells us little on how good sensors would be in, say, detecting weaknesses in an Imperial void shield or vulnerable point within the ship itself. The Borg cube clearly wasn't opaque to the Enterprise's sensors, Data could see the coordinates and believed there were other, more important systems elsewhere in the ship so presumably those were detected.
Without knowing exactly the weakness Picard was targeting and why it was overlooked by Data we can't say with any certainty what to draw from this.
It actually does factor. For the mainline TV shows, Star Trek ships have multiple weapons arrays but rarely if ever fire multiple arrays simultaneously
Actually I'm pretty sure we see the Galaxy class fire multiple torpedoes in a single go pretty regularly. The 23rd century century Defiant was a little slower but could shoot off four or five torpedoes in a couple of seconds when we saw it in the "In a mirror darkly" two parter.
Further even if we accepted your supposition, that would still only require two ships. Not a "large fleet" as Picard suggested. So whatever weakness Picard meant, which considering modern Trek is almost certainly going to be stupid, it wasn't because you could shoot both ships.