So I suppose you mean "Things that are easier to understand for novices [...]".
But that's not always the case which is incidentally proven by your examples. Assembly Language is a lot easier to write and understand for novices than machine code. And Fortran even more so. Bret Victor illustrates this very nicely in the video I linked to.
I'm convinced that the power that makes something more concise and at the same time easier to write and understand is abstraction. Or more precisely, the right abstraction, since a bad one can have to opposite effect. So I agree with you that better and more powerful abstractions are always good. Spreadsheets for example are a great abstraction for some problem but terrible for others.
So in order to "leverage powerful concept" and "express complex ideas" you need to be able to create your own abstraction. In this way my proposal is very different from Excel which barely allows to create any new abstractions.
What the manifesto apparently doesn't make clear is that I'm not proposing a new programming language but a programming model. The language part is more like byte-code than Java but it's really a protocol. The result is something that would serve a similar purpose as HTTP but would be vastly more powerful.
I think the mistake that these "language designed for children" that you have in mind is that they add training wheels instead of removing the pedals. The latter manages way better to teach you the basic concepts (steering, balancing) first and once you mastered these, gears and transitions increase your efficiency.
When it comes to software, I would take a similar approach and create a software authoring/execution environment that can be used by novices and experts alike. Novices would learn the concepts (message passing, abstraction) without actually writing code. The coding would then be added to increase the user's efficiency by providing a more concise notation. The actual language used would best be domain-specific to achieve maximum efficiency.