You're literally arguing that a government intelligence agency couldn't find a couple of experienced people, provide them with commercially-available equipment, and get them to coordinate a medium-complexity task.
Yes, it's an operation that requires coordination and planning, which is why it's reasonable to assume it was carried out by an intelligence agency and not a lone fisherman with a grudge. But once you're in the realm of intelligence activities, this isn't exactly the "let's blow up their pagers" level of complexity.
Their sabotage attempts of several bridges in Crimea did not go this well, suggesting that the Ukrainians alone aren't the best at understanding explosives, and their successes like "fly a bunch of FPV drones out of a shipping container" are quite a bit simpler than this. "Intelligence agency" is a spectrum of capability. Suggesting that an intelligence agency that tried and failed to blow up a bride twice was the same as the one that executed a flawless operation against an underwater pipeline is a bit far-fetched.
It's not at all obvious that e.g. the drone attack, which involved >100 drones assembled inside Russia by human operatives who were able to safely exfiltrate, and 5 different storage containers, in a coordinated strike on 5 different airfields hundreds/thousands of kilometers apart and away from the border, is a less complex operation than the destruction of NordStream
Snuggling and launching drones from deep within enemy territory is a much more complicated op than a couple of dudes diving in the middle of nowhere.
Bringing that bridge down is also much harder than blowing up the pipeline, because the bridge is covered by a lot of defenses, and naval drones will always have limited payload (if they want to be fast enough to evade defenses). Dudes performing a dive in the middle of the sea far from the battlefield are much less vulnerable.
Wait, NORD Stream was BEHIND enemy lines? And is as short a span as a bridge (so more easily monitored complicating things). How many people traveled across the Nord Stream pipeline a day that required the operators to be hidden from?