AmigaOS does in fact have several performance bottlenecks, discounting hardware completely, the OS is cooperatively multitasked, similar to Mac OS pre X, so a task that demands CPU time gets it, with no way for the user to interact with and kill the task. Similarly, the OS is lacking a thread implementation, which spells to me NOT-THREAD-SAFE. I have seen a few userspace implementations of a ptheads-type model, but this is insufficient in most cases. This means AmigaOS, bare metal, runs everything in its own process, which increases memory requirements, wastes CPU time and makes the OS feel slower.
4GB RAM is not sufficient in many cases, either. If I am rendering something in lightwave on my Octane, I am limited to using slower rendering techniques that conserve memory, simply because my Octane has only 2GB RAM. If I had 8, the max, I would not have to be as careful. Even if I were to to take the Origin and hook it up to a G-Brick, which can have over 8 times the RAM of the Odyssey GPU, with only 4GB between four 64-bit CPUs, is going to have issues. Before you call a false analogy and say that IRIX is bloated, I have many times the power of the most-decked out Classic Amiga, and MIPS R10000 CPUs and derivatives are in a class above any G4-based Mac, and if I had a quad 800MHz Tezro with DCD and 8GB RAM I would go toe-to-toe with a quad G5 Mac in benchmarks and expect comparable performance, for a similar reason that the Amiga edged out PCs in the early 1990s: the central CPU didn't have to be fast because the GPU was able to pick up the slack, combined with a DMA design based on, and designed with, networking in mind.
The fact is you can't brush off hardware advancement like its nothing at all - you have to adapt and advance with it. 64-bit is becoming the norm in the open source world - PC-BSD, DragonFlyBSD, Ubuntu and a lot of other players are dropping 32-bit support, it is a DEAD-END. Even ARM has the v8 specification now, a 64-bit architecture is upon us. I love my Beaglebone Black, but sooner or later I will sell it, and cope with the fact that 32-bit in the consumer and hobbyist market is running out of petrol and circling the drain.
The fact is the Amiga-NG platforms MUST evolve and advance, otherwise it will be pretty much history, and it will join its competitors, DOS,OS and OS 9 in the history books for good.