The problem is, while you can reduce the energy requirement by making the beams narrow, that increases the total number of sources by the same factor. When we say that there are between 5000-10,000 FRBs all over the sky every single day, we are referring to FRBs beamed towards us. If you apply a 10% beam, your energy requirement drops by 10x, sure, but the source count goes up by 10x.
Right now, we don't have a large enough plausible progenitor population, even at 1x, for these FRBs. It's a really fun problem.
[1] See, e.g, the Methods section in https://www.nature.com/articles/nature20797 (or https://arxiv.org/abs/1701.01098)
> power the world for three centuries
Our sun for example is emitting enough energy in all directions to power the world for 300 years (over the course of 300 years), and most of it misses us.
Our sun isn't particularly impressive in terms of energy and such compared to other astro-objects, so I feel like these kinda of events releasing so much energy are to be expected.
I think you're saying any amount of energy can be produced by any amount of power, if the amount of time is unspecified. Which is true, but not substantive.