That's an important detail, not all macro-ops are more complex than micro-ops, and most of our everyday x86 instructions are simpler than the more complex micro-ops.
But we can agree that the complexity ceiling is much higher on macro-ops than micro-ops, right? The µop you mentioned does one (vector) FMA operation on two (vector) registers and stores the result to RAM. While in x86, we have things like the rep instruction which repeats an action until ECX is zero, or the ENTER and LEAVE instructions to set up and tear down a stack frame. Those are undoubtedly implemented in terms of lots of micro-ops.
> complexity ceiling is much higher on macro-ops than micro-ops, right?
Other examples are crc32, sha1rnds4, aesdec, aeskeygenassist - the math they do is rather complicated, yet on modern CPUs they are single micro-op each.
> one (vector) FMA operation on two (vector) registers and stores the result to RAM.
It loads from there.
> Those are undoubtedly implemented in terms of lots of micro-ops.
Indeed, but I don't think it's complexity. I think they use microcode for 2 things: instructions which load or store more than 1 value (a value is up to 32 bytes on AVX, 64 bytes on AVX512 processors), or rarely used instructions.
But we can agree that the complexity ceiling is much higher on macro-ops than micro-ops, right? The µop you mentioned does one (vector) FMA operation on two (vector) registers and stores the result to RAM. While in x86, we have things like the rep instruction which repeats an action until ECX is zero, or the ENTER and LEAVE instructions to set up and tear down a stack frame. Those are undoubtedly implemented in terms of lots of micro-ops.