Nobody thinks there's a magic bullet, but you seem to imply that continuing with the wrong puberty will not leave lasting effects. Delaying is the least bad of three imperfect options. You're complaining about "putting a decision on the child", while taking that decision away from them, the parents, and doctor.
Simply waiting "until they have more time to be certain" is not a neutral decision; it's deciding cis and worsening the consequences if they're not. They're consenting to a medical procedure - not to sex - so the age of consent [for sex] doesn't apply; informed consent medical ethics do.