It's overly simplistic. For example, Haskell's do notation allows asynchronous programming in a linear "task list" (to use your phrase). Yet most popular imperative programming languages do not; one must instead use callbacks.
As to whether programming with expressions is fundamentally harder, I'm not so sure. Since Fortran, most languages have supported arithmetic expressions over primitive numeric types, since they are certainly not easier with an imperative approach (MOV, MOV, ADD, PUSH). Haskell allows one to easily take this further using arbitrary objects and algebras, for example, expressions with drawing primitives, parsing grammars, financial contracts etc. With a small amount of syntactic sugar, you can even make expressions that look exactly like imperative programming (Haskell's do notation).
As to whether programming with expressions is fundamentally harder, I'm not so sure. Since Fortran, most languages have supported arithmetic expressions over primitive numeric types, since they are certainly not easier with an imperative approach (MOV, MOV, ADD, PUSH). Haskell allows one to easily take this further using arbitrary objects and algebras, for example, expressions with drawing primitives, parsing grammars, financial contracts etc. With a small amount of syntactic sugar, you can even make expressions that look exactly like imperative programming (Haskell's do notation).