We have a reason for believing as we do. Do you have an argument? Do you understand how supply and demand work? Do you know what the E in RCE stands for?
It was more a point about the extremity of responses to changes.
Undoubtedly the changes will have some impact on the economy in a multitude of ways, some more easy to isolate and others so indirect it's hard to determine a precise causal factor.
My issue with your statement is as follows:
1: You've framed this the be outcomes at a apolcalyptic scale.
Many changes have been made to the game over 20 years, and while every change has an impact, it is almost always not apolcalyptic or as extreme as those who immediately cry out. If all of such changes were, we wouldn't be here. Making a measured and balanced argument is far more compelling and accurate rather than extreme ones which rarely or never turn out to be true and the proposed scale you have put forward, which leads to point 2:
2: You've already decided what you believe the outcome to be, and then cherry picked causal factors to form a path which leads to that outcome. It's not a very throughout analysis of the outcomes of this change, and entirely leaves out many other potential impacts that may negate to some extend the logical conclusion you have come to. For example, you've identified one potential outcome being that given that crafting is no longer a dedicated activity, and thus can be done by everyone at any time. From this, you've decided the conclusion of this is that therefore the value of crafted items will fall to zero MU because of this. This fails to include the following factors in this argument:
A: That any increase in crafting activity will additionally require more of the input materials relative over a given period of time, which will mean without the increase in appropriate hunting/mining activity, would lead to in part to an increase in MU for the base goods, which is either good for hunters, or more likely, be passed onto the end consumer by the crafters. Or, with increased crafting activity, and thus more availability of crafted goods such as but not limited to enhancers, hunting activity may increase, which may balance the increase in required input materials (regardless of whether passed onto the consumer or stomached by the crafters) resulting in no net change in MU (negating other factors)
My overall point is that your analysis isn't thorough enough to be able to come to the conclusions you have stated, to the extremity you have stated, and fails to include a number of other impacts, outcomes and effects that change things.