This is how I operate in most traffic jams, since I only own manual cars & it’s much easier on my leg.
I genuinely don’t even remember any specific scenarios where somebody merging in caused me to have to come to a full stop (where I wouldn’t have had to stop if they didn’t merge). Not saying it never happened, but it was so rare and unnotable that I don’t remember.
I do live in the northeast US, so maybe that has something to do with it, but I don’t usually feel like I spend meaningfully more time in traffic because I let a few people in front of me.
Bonus benefit: my life is measurably better since I stopped getting pissed about people being in front of me. Road rage had such a broad impact on me, even after I got out of the car.