This is true. Cats that have been neutered take up resources that would otherwise be used for breeding studs or queens, thus making it more difficult for breedable cats to make their way into a colony.
TNR is a very effective way of managing urban/suburban feral cat colonies, and if you can find a local one to support, I recommend doing so.
Further PSA: This does not apply to cats in Australia. The RSPCA is still coming up with a position on this strategy here, but it is unlikely it will work in an Australian setting.
The greatest problem stray cats cause in Australia is a threat to native species who have no natural defenses against a predator like cats. This is doubly true for feral cats living away from urban centres, who cause massive damage to the local ecosystem.