the montessori method can handle larger class sizes specifically because of the way it is designed. in other words, large class sized are an even better argument for why the montessori method should be used.
When we transitioned our charter Waldorf to a public Waldorf, the kids experiencing it for their first year absolutely thrived. I would love to see both systems expand significantly in the public space, and have educators with enough savvy to help kids find their best place.
I think that even a more traditional school system can be totally healthy, and should stay part of the school mix. I have seen it work out relatively well in other countries. It just doesn't work when run like a for-profit prison.
I'm not saying that kids cannot have a good experience at a Waldorf school, or that all their educational ideas are bad. Just that once you children have been there for a couple of years, you learn some very disturbing truths about the organization. It's not an education institution as much as it is a religious organization - your children WILL be taught hymns about god and angels in class. The teachers will not admit to this. They will be taught from the original lessons of Steiner, who had some rather unconventional pseudo-scientific ideas (even for his day). This is coming from a dad who had his kids at Waldorf for three years, and I'm so glad I finally got them out - even with the difficult academic transition.
There is plenty of information published about their organization online, and growing awareness worldwide.