First, it might be 'a lot of scientists' in absolute terms because this is such a fertile field, but it is a tiny minority of cosmologists who believe MOND is t

First, it might be 'a lot of scientists' in absolute terms because this is such a fertile field, but it is a tiny minority of cosmologists who believe MOND is the best explanation for these effects. Secondly, even the proponents of MOND concede that you need to introduce some amount of dark matter in order to explain e.g. observations of the Bullet Cluster. So the competition isn't between new particle vs MOND, it is between MOND + new particle vs new particle.