Linear BEC`s usually are able to deliver 1-1,5Amp only.
The small servoes we use in our small toys have large differences in how much amperes they consume. This means that 3 servoes are not 3 servoes... The difference in current consume could be huge!

I have some Graupner servoes, and they have good specs telling everything:
The C261 is a beauty for depron, and draws max 450mA.
The DS281 is a digital beauty with same specs appr, and draws only 285mA max. Digital, and half the amperes.
But the DS361 which is digital too, slightly more torque but a lot more of holding power draws max 610mA... Digital and 50% more amperes.

Then you get a standard servo like the C577 which is at less than 900mA. Although it weigh 5 times of the small ones [X(]

People often think that small servoes use little current, but it is not true. Either you should buy servoes where the specs are given, or you have to measure it yourself. Be prepared for surprices.

BECs usually cut out when the consumption is too large, or temp gets too high. Don`t think this is related to spesial BECs.

Don`t know the S-75 servoes, but I have not heard they are worse than others.