I find two fundamental efficiency points- into the kettle (getting the wort gravity right) and into packaging (volume). Others are secondary (not that they don't matter, but they're important in leading to the two above).
For example, if you're just dumping all your trub into your fermenter, your batch size and brewhouse efficiency will be higher on paper than someone who leaves the trub in the kettle, but when it comes time to package you leave it all in the fermenter and you may end up packaging the same amount of volume, so that efficiency increase really didn't exist at all. Or if you're converting 100% of the mash but leaving sugars in the grains, you're also not very efficient.
From there, my view is that wort properties are far more important than final volume. So I dial in efficiency going into the kettle. To me hitting my gravity is paramount to how much wort/beer I end up with.
You still get variance with conversion/lauter efficiency based on gravity and how well you sparge, but that's far more predictable than hop/trub/yeast loss. If you do same beer enough times you can even notice a change between different lots of the same hop (and not even just adjusting amounts for changing alphas, different sources and lots absorb more or less or compact more or less tightly changing how much clear wort/beer you can get out).
I think the "no-sparge BIAB is less efficient" idea came from when it was thought to be harmful to squeeze the bag, which has been shown (at least by perceptive standards) to not really be the case. As said above, this drives BIAB grain absorption (and the sugars with it) way down.
Now, I haven't done a BIAB batch in a good number of years, and I believe I used to get lower 80s efficiency into the kettle when I did (but I also squeezed and sparged). I get in the lower 90s efficiency into the kettle using a traditional continuous sparge (on a standard gravity beer, if I go big it'll dip into the 80s or if I go upwards of 25°P I'll hit the high 70s). However I can't confidently say if that's inherent to the process or if I'm just a better brewer than back when I did BIAB.