Decompilation is primarily intended to be consumed by humans, I.e. to make the assembly more understandable because it’s written in functions, ifs, and for loops; it’ll likely not compile at all and if it does not to the original firmware. I don’t believe it’s typically an explicit goal of decompilation to be that high fidelity (ie allow recompilation). It’s probably possible to hack the source to compile to byte-for-byte the same firmware if desired with a little patience.

Other than that, you’d be right :-)