Changing physical characteristics to align with gender has a comparatively strong evidence base for adults, and strikingly high satisfaction rates. Blockers are just a slightly different (and more effective, in terms of appearance) mechanism of achieving the same thing in children.
This isolated framing is imo an intentional choice by cass/segm to make the evidence base look worse. The standards for extending a successful treatment in adults with well understood interventions (physically speaking) to children SHOULD be lower than for an entirely new treatment.