I think it depends on the amount of 'genuine' trans individuals vs those somehow pulled into it by social currents.
If 7 out of 10 go for transition for the wrong reasons, then banning blockers could be the right choice statistically speaking.
Not saying I think it is 7 out of 10, but I am sure the number of those who transition for wrong reasons is higher than zero.
Also, don't they start giving blockers to pre-teens ? Your cancer analogy refrred to teens