Sometimes you have to change and sacrifice stuff in order to make a better product. Specially because noone at RT expected for RWBY to blow up the way it did, specially being their own IP rather than one based in another company's property like Red vs Blue.
Monty was always one that liked to challenge himself anyways, so a lot of people (me included) feel that yes, he probably would have been intimidated but would have recognized Maya needed to come eventually.
Also, as other people pointed out, Monty was aware that he was good at creating ideas, but horrible at writing characters or story. He even mentioned that when he came up with Team RWBY, he had the designed and basically nothing else and had to work with the others in coming up with actual personalities and characters. (Probably why the original Red trailer is so different in tone; that was simply the animation pitch and nothing of the actual writing had been made).
Monty specifically picked Miles and Luna to write scripts knowing they were at least better than him (opinions on their writing prowess aside). So the fact Shane kept going with everything Monty said as gosspel is even more baffling when Monty himself never felt that way.