Do you think it's a definite flaw to have only a few girls?
Yes, for a number of reasons.
1. The new agencies that I've seen seem to have 3-4 girls working 6-7 nights per week. I personally don't think a girl should work more than 3-4 and, in most cases, each will have to take the better part of a week off every month. So, if you have 3-4 girls on your website, they will either be working too much or only 1 or 2 will be working on a given day.
2. In the case of 3-4 girls working 6-7 days a week, there are quite a few clients, myself included, who don't want to see a girl who is overworking. She will most likely be working without much desire and without enthusiasm. If you have only 1-2 working, you're not going to generate enough calls to make a living as an operator.
3. Many clients, and I'm not including myself here, do not like to repeat with a girl. If your roster is limited to 3-4 girls, you will find it near impossible to develop a repeat business with most clients.
4. Most failing agencies with small rosters have the same lineup they opened with months later. If you want to stay in business, you need to constantly recruit new talent. You can't do that if you have the same boring website with the same tiring lineup you opened with months earlier. The best way to recruit new talent is to have girls refer friends; if you don't have a lineup to start with, you don't have that avenue of new talent.
Of the agencies that have opened in the last year, only Chloe's/Candyshop seems to be making regular additions to their lineup. And I'll bet they're the only new agency to survive. There is work involved in running an agency and what I see from the others is laziness in the lack of recruiting and lazy websites. The agencies I mentioned above have, for the most part, been around a while, have set the bar pretty high for both service and offerings. A new agency that wants to compete will need to give the potential client a good reason to try them. That starts with a strong and deep lineup, regularly refreshed, and continues with good customer service.