Stone Mill, you think too much in the short term.
Of course they are less efficent immediately. That is where the balancing comes in. But in large epic games, going with Monoliths is pretty much always a better idea. Such games often have long periods of peace, and those periods are good for getting Monoliths going. Compare Monolith III with Miner III, 2700 (or 1800 of one resource with converter Is) to 1000 resources. In the long term, Monoliths really pay off.
I never advocated Monoliths in small games or in the early game, btw.
And naturally, Monoliths go hand in hand with Resource Converters.
And yes, Monolith I and II are not very useful, which is why I never build them.
Also, SY III + HI + 120 const. apt. gets Monoliths in 3 turns on low pop worlds, and in 2 turns on high pop worlds. Take Organic, and you can make all planets high pop worlds (well, large and huge ones, at any rate) in no time.
Temporal is not the only way to get fast construction rates.