Refer to noise-normalized measurements (as pointed out in the parallel thread), which covers also the reverse question. IIRC the lack of rear fan utility with a top exhaust AIO’s in there too.
If the objectives are low price-performance and supporting walled gardens, sure. FWIW my experiences with iCUE have also been pretty poor and that’s without even needing to use it for lighting.
Eh, it’s not that big of a deal if the cheap fans turn out to be a wee bit too loud. Most of the time.
It’s like complaining about having to drink a $50 Prosecco instead of real bona fide $200 Champagne, if you want to be a snob, fine, but the majority of the people will take the money savings thank you very much. 
That’s not to say more premium brands do not give a better experience, just that Corsair is good enough for many people. That said, Arctic is another brand that is worth considering in the budget category, and I would go with Arctic fans over Corsair fans personally.
Yeah. Entry level for an iCUE fan is US$ 34 here. Momentum 12 RGB is US$ 28. But P12 Pro ARGB outperforms it for US$ 9-10. ¯\_(ツ)_/¯
IIRC Uni Fan TL is quite good as a fan but US$ 45 each? 
140mm fans move more air, are generally quieter per unit of air moved, and move more air over a wider area. Larger fans tend to lower frequencies as well and often they are better balanced.
A corsair fan moves 28% more air 120mm vs 140mm. But the 140mm fan tends to be less good at static flow.
140mm fans are idea to move air into a case, out of case. 3x140 fans will do the work of 4x120mm fans.
120mm fans tend to be better in static flow, so smaller fans are often used on GPU’s, CPU’s and radiators. Although for a radiator 140mm fans are still very effective, and may be more effective just not quiet as effective as moving air freely. Their is a 14% difference between static and free in favour of the 120mm so in a static push, the 140mm advantage is more like 10-15% rather than 30%.
Some people love 140mm fans and acquire cases for them. But those cases tend to be larger. For a compact mATX build 120mm fans are fine
Flow is, by definition, not static. Recall from fan fundamentals that static pressure is measured at zero flow.
You’re correct 120 mm fans tend to provide greater noise-normalized airflow than 140s at higher flow restrictions. Corollary to this, the claim “A corsair fan moves 28% more air 120mm vs 140mm” can, at best, be true only for only two operating curves and is thus usually going to be incorrect. On a noise-normalized basis it’s more or less guaranteed to be erroneous. Similarly, it follows “140mm fans are idea [sic] to move air into a case, out of case.” is broadly incorrect though, depending on the designs and flow resistances involved, an optimum may occur for particular 140s in certain cases if the other fans in the build modulate the flow resistance in the right way.
Recall from fan fundamentals that pressure from fans in series stacks. I’d suggest the interesting design question here is whether current gen airflow cases are low enough flow resistance to take advantage of 140s. But, unfortunately, there isn’t data to answer it because nobody measures flow resistances.
On a noise-normalized basis for a parallel arrangement? Likely only if parts selection is incompetent. Since not that many cases are large enough to take 4x120 front a more common question is 3x120 versus 2x140. Which has a stronger version of the same answer in noise-normalized airflow.
But, since airflow doesn’t completely mix in an ATX case, which front fans matter how much depend on installed components, workload, and airflow configuration. Like with 3x120 front intake and idling dGPU decent chance you can shut off the bottom 120 and not see measurable temperature differences in a CPU only workload.
So ideas such as 3x140 and 4x120 needing to do the same work have a way of not being well posed and are thus best used with caution, if at all. For example, if the 28% thing was actually correct you’d have 3 (1 + 0.28) = 3.84 < 4.00.
If, by frequency, you mean RPM and thus blade pass, yes. Otherwise not necessarily. For the second claim, vibrations in most fans at most speeds are below third party measurable levels for the few reviewers that look at them. So, unless maybe buying crappy 120s is specifically the objective, there’s a lack of supporting evidence.
Normalised for flow. To flow the same, the larger fan can spin lower. The RPM speed creates sound frequencies based on those cycles. Lower fan sound frequencies tend to be less annoying than higher frequencies. Particularly if you are almost outside the range of human hearing.
Yes, that is generally what people focus on. Noise, or cost. 140mm fans perform pretty strongly in that space moving decent air at lower less annoying RPMs.
Its corsairs claim, not mine. They sell 120mm and 140mm fans, so that is their input.
Doing a bit of AI data gathering…
140 mm vs 120 mm (at their rated max):
ARCTIC publishes current at 12 V, so P≈V×IP \approx V \times IP≈V×I.
140 mm vs 120 mm (at their rated max):
So 140mm fans do tend to flow more for same power use. Many cheap 140mm fans, use more power so can flow a lot more than cheap 120mm fans. Noctua is 30% better, cheap fans its like 8% better.
But this is just looking at stated figures at max power/max flow. Lower flow it may get more complicated, but I presume for a given RPM you will get less flow out of a 120mm fan.
Moving to 140mm fans is quite popular now.
I would think so, they are essentially all mesh now. Cases like my Lian Li A3 are entirely mesh. The only one that have more sealed airflow are glass side panel cases.
But as always, your application and situation may differ. Server cases tend to be pretty sealed and follow a direct flow path style of design.