Like the CNC machining meme. If you reengineer society so that everyone below the top 5% of their high school class becomes a CNC machinist... it's not going to be a rare and valuable skill anymore.
On the surface it seems like you're arguing that there is not enough room in the trades for more tradesman. However adding a good chunk of people to the trades will increase the velocity of money in the form of more people spending more dollars based on their higher salaries. The alternative is that the demand for trades is fixed, which doesn't make much sense to me.
The demand for trades may not be fixed, but it is not proportional to the number of tradesmen. Most likely it's proportional to overall economic activity in some way. Doubling the number of tradesmen will not double economic activity across the whole economy, or likely have any significant impact on demand for tradesmen, so the value of tradesmen will drop until some are forced out and an equilibrium is reached, probably not far off where it is now.