Not exactly subtle.
. And then you find out sound is still lacking, or "why do I hear 2dB of more bass between these channels when they measure the same, but only have different opamps"?
The bottom line is, the choice of opamp will make a remarkable difference in sound.
Sam's opamp testing reveals how they work under ideal conditions and I would advise caution about trying to impute too much from how they measure in his tests to how they will behave in a given circuit. While an experienced designer will extrapolate and make predictions based on several different opamp parameters.
The transfer function of 99.9% of opamps used in consoles is defined by negative feedback networks. There will also be secondary effects related to power supply quality, and even integrity of PCB layouts (crosstalk, ground corruption, etc).
There can be measurable deviation from the transfer function commanded by the NF networks if opamps are used with inadequate open loop gain for the NF closed loop gain commanded. The widely used TL07x can be marginal for OL gain at 20kHz if used at higher closed loop gains... The nominal benchmark measurements in Sam's overview does not reveal the whole story, of how they act in every circuit. Hypothetically substituting an opamp with more OL gain for a TL07x in a marginal design could improve compliance to the original NF network, but if the original designer tweaked that NF for flat with the TL07x, the new better opamp will now deliver too much gain at HF.
The vast majority of audible differences that are "not exactly subtle" are not exactly hard to measure either. Hook up a simple sound card with signal generator and metering to measure basic frequency response.. More often than not, "remarkable" sonic differences are very apparent in basic bench testing. I have measured many differences that I couldn't hear, but never heard a difference that I couldn't measure, while back in the day I did dabble some in DIY test equipment, to refine my bench measurements well beyond what I could hear.
Swapping out just the opamps without consideration for the components and other contributory factors around them can deliver variable results. A more scientific approach, should lead to more reliable forward progress.
PS; While not a perfect analogy swapping out opamps is a little like bolting better carburetors on a car motor. It may work better, it may not... Even a significantly better carburetor, without adequate fuel flow, increased intake valve lift, optimal ignition timing (a denser charge burns faster), manifold flow, etc. will not magically live up to it's capability.