Point 1 has come up in at least one form I remember. There was an interesting discussion some while back about limits to the speed of growth of new computer hardware cycles which have critical endsteps which don't seem amenable to further speedup by intelligence alone. The last stages of designing a microchip involve a large amount of layout solving, physical simulation, and then actual physical testing. These steps are actually fairly predicatable, where it takes about C amounts of computation using certain algorithms to make a new microchip, the algorithms are already best in complexity class (so further improvments will be minor), and C is increasing in a predictable fashion. These models are actually fairly detailed (see the semiconductor roadmap, for example). If I can find that discussion soon before I get distracted I'll edit it into this discussion.

Note however that 1, while interesting, isn't a fully general counteargument against a rapid intelligence explosion, because of the overhang issue if nothing else.

Point 2 has also been discussed. Humans make good 'servitors'.

Do you have a plausible scenario how a "FOOM"-ing AI could - no matter how intelligent - minimize oxygen content of our planet's atmosphere, or any such scenario?

Oh that's easy enough. Oxygen is highly reactive and unstable. Its existence on a planet is entirely dependent on complex organic processes, ie life. No life, no oxygen. Simple solution: kill large fraction of photosynthesizing earth-life. Likely paths towards goal:

1. coordinated detonation of large number of high yield thermonuclear weapons
2. self-replicating nanotechnology.