With the motorsport types, they even had the Nissan GT Academy thing, and some people have gone from sim racing to become pretty reasonable pro racing drivers - Lucas Ordóñez and Jann Mardenborough are two notable examples.
Actually it's probably possible for your 'zwift pros', if they are trained to a pretty good level, to have the ability to put out elite wattage, at least over the shortish period of time that these events are running for (they aren't doing this after five hours already in the saddle as they ordinarily would at de Ronde!). The main thing that separates the motorsports pros from the e-sporters is the same thing that separates the cycling pros from the Zwift types, and that's the mortal fear factor. I know the sim racers out there buy the big VR setups and get the steering wheel displays and everything so they're totally immersed in the world they're in, but you always, always know that you're in no real danger. You could bin it at Eau Rouge, or the Kink at Road America, or the old version of the Peraltada, and in a VR world that might seem scary... but there's no actual impact on the end of it. You can race more aggressively and keep your foot in it longer because while reckless ploughing into another sim racer in an important event might carry social implications, you aren't actually at risk of injury.
And so it is with cycling. One of the most important things about road cycling is that it is a pack sport. You have to learn to ride in groups, going at fast pace along narrow roads with another 100 riders in proximity. That downhill section that, on Zwift, represents a nice breather, might be in real life a stressful, tense experience with the risk of grave injury at every corner if taken badly, and many pro riders will have seen or experienced a friend or colleague dying in such circumstances. Tactics are a major factor, of course, which it is impossible to replicate in a virtual environment. Yes, they do a great job of changing difficulty settings based on wind, gradient, slipstream and so on, but you can't take a turn through your group and actively see something in the expression of your breakmate that tells you something. Even if they're on cam. Mother nature is another difficult to replicate factor. We all know of certain riders favouring certain conditions: Froome excels in cloying, hot conditions. Ian Stannard deals with real cold and heavy wind and rain better than most. Tim Wellens is rejuvenated by bad weather. Quick Step as a team being the kings of the echelons (another thing it's difficult to replicate - team moves can only be done up to a point in a virtual environment).
For another pointer, you could also look at Leah Thorvilson, who won the first Canyon Zwift Academy program, as the best performer of over 1200 participants. She had pretty good sporting pedigree to do so - she's a former marathon runner who qualified for the US Olympic trials in 2012, so she's got the background that would explain her strong power levels sustained over a long time. But in two years as a professional on Canyon-SRAM, a strong women's team, she scored a grand total of 7 CQ points - those for finishing 97th in the Ladies Tour of Norway, which is a WWT race, and 36th in the 2.1 Tour of Belgium. She DNFed over a third of the stage races she entered, and was outside the time limit on the La Course edition that finished on Izoard. After returning to the US to enter domestic cycling last year, shorn of the elite professional support team of Canyon, she struggled to finish races. This isn't to dogpile on Leah, who was clearly an athlete at a high level before she did the Zwift Academy, and was likely put into an environment that she would easily be overawed by - she would invariably have been used as a domestique in a team with the likes of Lisa Brennauer, Kasia Niewiadoma, the Barnes sisters and Pauline Ferrand-Prévot - but it shows the difference between having the power and the ability to transfer it into a professional racing environment with all of the additional factors that are at play.
Or, in another sense: Dave Brailsford's band of merry men took nearly 2 years to get the hang of this road cycling lark, adapting what they already knew and had mastered from the track to the greater number of variables and the vagaries of road cycling. They did it, and have parlayed it into a decade of domination, sure - but the first year was a catalogue of examples of bluster and PR self-aggrandisement going wrong when confronted with situations that were not as easy to control as expected. And that is from an entire set-up of people who were already professionals, excelling to the point of domination in a different area of cycling. It's only reasonable to expect any such Zwift pro to require a lot of adaptation time if they did manage to reach such a level as to turn pro.