This is just to bust the myth (very popular among some members here) that if you install a full exhaust on Multistrada 1260 the bike will run lean. THIS IS NOT TRUE! Stock ECU perfectly compensates the difference. If nothing else, the bike is actually running a bit rich.
Trimmed for easier reading.
I don't have a dog in this fight one way or another, but I don't think it's entirely accurate to extrapolate the conclusion reached from the data provided. A dyno run is performed by taking a vehicle from idle to wide open throttle (WOT) in smooth but rapid fashion, and leaving it there until it reaches max RPM. At WOT, a fuel injected engine is running in open loop injection mode, ignoring the inputs of the oxygen (lambda) sensors, vs closed loop where the o2 sensors are used to fine tune the fuel/air ratio in near real time. The A/F readings on a dyno chart are provided by a wide-band o2 sensor placed inside the exhaust by the dyno operator. Closed loop is used during partial throttle application to achieve better emissions and gas mileage, while open loop is used during WOT to ensure the safe operation of the motor.
In other words, while running WOT, a fuel injected engine is running a fixed timing map read directly from the ECU. Changes to the exhaust system will have zero impact on this fuel map, so the only way a cat-less exhaust could make an engine run lean WOT would be improved harvesting from the head, combined with imperfect valve control. Not to mention, since every production vehicle uses an open-loop map that's a little bit rich for engine safety, even if those conditions existed, it still wouldn't likely result in a critically lean engine.
Partial throttle, though, is where we run into a problem without a tune, and sometimes even with one. The factory lambda sensors are programmed to operate within a range; being narrow band sensors they can't cope with oxygen levels that are way outside their normal operating condition. With a catalyzed exhaust these sensors are between the head and the catalyst; a controlled environment where such a narrow band sensor can work well. Remove the catalyst, and that sensor is open to the world. The level of oxygen detected by said sensor will increase, often outside it's operating range. If so, the ECU will throw a code, but if not, the o2 sensor will tell the engine that there is unused oxygen in the exhaust (lean), and the ECU will send more fuel to the injectors. So the common result of adding a cat-less exhaust on an untuned engine is an over-rich mixture during non-WOT operation, and a resulting net loss
of power, not to mention a filthy running engine that gets poor fuel mileage. Most tuners will not resolve this issue either, because they only interact with the open-loop tables. In fact, many tuners disable the lambda sensors entirely, defaulting the closed-loop tables to under-timed settings designed to protect the engine. RapidBike is an exception in this area, at least that's their claim.
This is a complex topic and I'm certainly not suggesting everything you posted is inaccurate, I just don't think it paints a complete picture. In all likelyhood, if an owner installs an uncatalyzed exhaust on their MTS without a tune, they will experience no issue at WOT, as your dyno runs indicate. During partial throttle application, the engine will probably run rich, make less power, get poorer fuel economy, and have somewhat lower exhaust and engine temperatures due to the rich mixture. This isn't a condition likely to damage the engine, true. On the other hand, there are secondary changes that come with an uncatalyzed exhaust, such as those lower exhaust temps, that can have an opposite effect on the lambda sensors, resulting in a lean condition. How closed-loop fuel management deals with all of these parameters is basically unknowable to the layperson, so while we can say it's not normal for removing the catalyst to result in a lean condition, it's certainly not impossible either.
tl;dr: Unless you plan on running WOT all the time, you should get your race exhaust system tuned, and use a system that can work with the lambda sensors, not just disable them.