1) I'm looking at the Catalyst's premise. The argument is that Organics make Synthetics to improve themselves and those Synthetics kill their Organic creators. if the Reapers give Organics the Synthetics, then Organics have no reason to build Synthetics.
Fair enough. But then, once the Reapers have given organics the synthetics, why would they need continue existing? Maybe they'd head off to Andromeda or something to spread their "safe synthetics only" doctrine (oh, f*ck no!). There is nothing to indicate that giving a species synthetics and saying, "Those are all the synthetics that are safe for you to have," would stop anyone from experimenting further. For example, it certainly wouldn't stop TIM imo.
2) The Catalyst's Reaper solution doesn't address the root of the problem either. However, my proposed solution #2 doesn't kill lots of the organics.
The crisis that the Catalyst claims to be averting is the destruction of all organic life at the hands of synthetics. To the extent that the Reaper solution allows organic species to continue to develop (up to a point), the Reaper solution does work - at the expense of advanced organic civilizations, yes.
Are you suggesting that the Reapers show up to kill super-synthetics whenever the latter appear, then retreat back into dark space to wait for the next batch of super-synthetics to appear? I could envision this happening if Control is chosen.
3) No it doesn't. The closest species that came to creating the super synthetics is the Quarians, yet the Reapers come to harvest everyone else who has advance to whatever level. You even said "species sophisticated enough" meaning it doesn't matter if they actually did it or not. I'm suggesting only killing off the species who did it.
To use an extreme example, are you suggesting that all humanity should be harvested by the Reapers because of Project Overlord?
If the Reapers leave alive a species capable of sentient synthetic construction (but who has not done it yet) and retreat to dark space thinking their work is finished, that species could then begin development on a sentient synthetic immediately after the conclusion of the harvest. Meaning that, by the time the Reapers arrive for the next harvest (even assuming 50,000 years is an estimate), all organic life could already be extinguished, meaning the Catalyst failed in its mission to protect organic life.
On that note, why do the Reapers go away? Why not constantly patrol and police the galaxy? If they need sleep, they can take shifts.
Patrolling the galaxy could work, as you suggested, though I speculate not for long - primarily because species would resent the Reapers' patrolling as controlling and not liberating (not that it would necessarily be one or the other).