Like anything else USCIS, YMMV. As the processing times for the N400 at Columbus is 11 months, you may hear something soon on that. In the end, if naturalization is the final goal, why wait to file the N400 as in the end, that is all that matters and the I751 becomes just a necessary evil. The files will not be connected until an IO at Columbus starts actually working on your file and requests it is linked to the I751.
In the end you are correct, if anyone is simply filing the N400 to speed up the I751, they may find it does not work (similar to those filing the I129 for a K3 after filing an I130). I know in our case, it may have sped things up by a month or so, but my wife did not file the N400 due to her languishing I751, she filed it to become a citizen, and she became a citizen around the same time others that filed their I751s during the same period were getting their 10yr GC.