I agree, Sentient robots should be creatable, but at least from a lore/meta standpoint you dont start with that level of tech. I'd rather see an origin or civic that allows for playable sentient robots but thats just me. Synthetics should 100% be a thing though, when we get the tech to make robots artificial skin is a stones throw away at most.
If we're complaining, I'd like to complain about how influence is the eternal bottleneck for everything. I can't use the subterfuge mechanic at all, not only because it's at best mechanically weak, but because it costs influence to do anything. I use it passively with envoys, but even that is worthless unless you have some good codebreaking going. I suspect smaller empires can use it more because they spend less time building megastructures or expanding or claiming. It's not that I dislike there being a bottleneck, it's that it prohibits gameplay.
I'd like to see something where perhaps you have a new passive mana. In civilization IV the spying mechanic was not perfect, but it worked well enough to have some use, and it stayed out of your hair if you didnt want to engage with it. Spying is super abstract in Stellaris, so I wont get into specifics, but in general more contact through borders and diplomacy, more chances to spy. Some technologies lend themselves to spying more than others. One benefit of a xenophobe or closed society should be spy protection but not necessarily lowered offensive spying applicability. Just some system that incentivizes engaging with established mechanics. Most of the operations are nuisance stuff, so make it more accessible.
Perhaps using other kinds of mana in conjunction with influence instead of straight up influence. Hell, knowledge is a really abstract science thing, maybe some biology research can go into an operation. Larger empires generate more points, and it isnt unfair that each individual point is worth less to them than smaller ones....
I like the idea of influence in general, but the struggle is real. It costs me hundreds of influence to change a subject to integrate them, and hundreds more to actually integrate them. It's wild to think that in 2300 I still have a couple dozen unsettled stars in my back field from when I murderkilled and/or outexpanded my competition to chokepoint that stuff off.
P: and ethics! We have random leaders heading factions now. Just make some system where leaders espouse ethics based on where they are stationed or if nothing else their home planet. Let spys interact with leaders and push ethics. adding ethics attraction modifiers from spys would give us more use for spys, let peaceful builders do more, and could help us destabilize the blobs more. It also lets you have a 'defensive counterspy' job maybe, and lets you do thing anonymously.