The official explanation of the technique never really reflected its actual usage in practice. Everyone agreed that, in practice, the substitution Jutsu is basically teleportation, but we didn't index that way because people were against "ignoring the official explanation".
Regardless its mechanics, however, the technique clearly works even if the user is completely immobilized.
- Here it is being used while Pain is literally encircled by Jiraiya's hair.
- Here it is being used by a Madara who was caught within Gaara's Sand Mausoleum sealing Jutsu.
- Here it is being used by a Madara who was caught by Naruto and Sasuke, and immobilized by Naruto's sealing Jutsu.
It should be noted that in all of these cases the Jutsu is being used against people who are comparable to the user in speed, if not faster in the NaruSasu example. Furthermore, Naruto and Sasuke have several layers of sensory and precognitive abilities, so them being blitzed by Madara's raw speed just doesn't work. The technique just "works", for lack of a better term.
- Reverse Summoning Jutsu does not prevent him from being BFR'ed again
It doesn't, but that kinda creates a bit of an Incon situation, especially because Madara can't be incapacitated due to his regeneration and infinite stamina.
- Izanagi can reverse the BFR.... and then he can be BFR'ed again
Same as above tbh, because the Rinnegan negates Izanagi's cost.
The Genjutsu he used on randos and on A was to paralyze them and Garou can resist paralysis inducement. Has he ever used complex illusions in the middle of a fight?
Madara is not stupid. If the paralysis doesn't work, he'll switch to a different flavor of genjutsu. Also, his genjutsu is layered, so it could just work against Garou regardless.
And yes, he has used more complex applications before. He used complex illusions against Obito and mind control against Kurama.