I don't run counter to an army of engineers lightly.

What you say about the float accounting for the inconsistency of the system is correct enough (as long as you meant to say the cable system rather than the drive system; the cogs don't move sideways) - as far as Shimano's 9s and 10s systems are concerned, because their cable pull is short enough to be corrupted far too easily, although I've run S9 quite reliably without a floating jockey wheel. With S9 I've found adjustment just requires a finer touch and can take a little longer to finish bedding in, but I can see it being a necessary evil with S10... I've only shifted 10 cogs with SRAM so far, though.

Let's break down the cable maladies and see how they relate, huh?

Housing mush/springiness: cheap or damaged housing will give the lever a rubbery feel, making shifting inaccurate, and sometimes requiring the cable to be pulled past the click to make it to a bigger cog despite the cable tension being correct. S9 and particularly S10's inadequate cable pull magnify the mushiness of even good quality housing too much IMO (I've seen a S10 RD not even move when the cable was pulled). So housing issues mean the cable doesn't get pulled far enough at the derailer, in general.

A floating jockey wheel makes this symptom worse, requiring more cable pull again to make it to a bigger cog.

Excess friction: too much between cable and housing makes shifts to smaller cogs hesitate or fail, and again, this is magnified by a system designed with insufficient cable pull. Friction dramas mean the cable doesn't get released enough at the derailer, and when it's pulled can make the lever feel stiff, and introduce more inaccuracy via housing mush.

And a floating jockey wheel makes this symptom worse, requiring more cable released to make it to a smaller cog.

All the floating pulley is good for, is to make up for slightly off cable tension adjustment. In fact, it even masks slight maladjustment, which without a floating pulley is more easily detectable via the sight and sound of the chain running on one cog, but with one you need to compare upshifts to downshifts.

Because the pitch of threads on barrel adjusters can only be so fine, dialling in a modern Shimano system is a fine line - IMO that's the only point of Centeron-G, which as far as I can figure and observe, only hurts shifting (I know, it's been around since 6s, but indexing was a new concept then so Shimano probably figured a fudge factor would help, and it was less of an issue with much greater cog spacing).

Even more useless on Campy with their decent cable pull; they were probably just copying features when it came to that one.

As for SRAM's entirely floating derailleur, I had a 10s one that was really shagged and every pivot was sloppy, so I'm not sure what the deal is there... is it a tad of side float on the upper pivot? If so, dumb feature; SRAM has miles of cable pull and their RDs are super easy to dial in.

You might as well sell a car with wobbly steering just cause most punters don't aim straight.