[2023] This is a lie. I have been on the defending side in Rush four or even more times in a row. This was supposed to be fixed since Season 4

Correction, this is not a lie. You are referencing Update Notes from Season 4, we are now in Season 6. Things change frequently with a Live Service game, not only in reaction to balancing concerns but also to technical or just general feedback from players.

As of Season 4, it was indeed possible to remain within a lobby and it would place you on the opposing side of the conflict. This has been changed recently to allow for more matchmaking opportunities and to ultimately help in resolving the fact that players were not able to join at the end of a round. Which if kept the same, would have resulted in more AI in Round Two.

This change has for the most part been a healthier change for matches, despite not being able to play round two.