If it's development speed you are after, practice. The more you practice and know your language and its applicable patterns, the speedier you get.
Which means, if these engineers train with frameworks all day, then of course they will be faster writing a prototype with them. Is that the right way? Maybe, sometimes, for specific cases, as outlined by the framework's problem domain.
However, if they used the vanilla trinity only all the time, they'd be writing their prototypes at just the same speed without frameworks, and at the same time keep basic web principles valid, which means they profit from established standards and achieve great compatibility with many users. That's especially important when you factor in that in many situations, the prototype becomes the final product - no re-write.