I'd imagine Nerve stapled soldiers have all the disadvantages of non-intelligent robots (poor initiative and ability to deal with unexpected situations) with very few of the advantages like not being squishy meat bags who need a generation to raise fresh troops/much more complex machinery to vat grow them than what is needed to manufacture a robot and are vulnerable to all sorts of nasty things like disease, radiation, and blood loss. Nerve stapling alone wouldn't make for very good soldiers, you'd need to put in more biological enhancements to turn them into proper super soldiers than just making them meat puppets.
And on that note, Robot, Droid, and Synth armies could all do with a buff beyond not being limited by your pops in number (I think anyway). Clones being able to be cranked out faster than mechanoids just seems kind of weird to me when in the most famous Robot vs Clone war in Space Opera the Seperatists' droid armies definitely had an overwhelming numerical advantage over the clones while the clones were more of an elite force; though both could be cranked out far faster than normal recruiting given the same population pool access. Seeing it be the other way around in Stellaris where Synth armies are the more elite force while Clones are a spammable horde just strikes me as wrong, it's not a big complaint it's just a bit counter-intuitive
