Separating the word 'meltdown' from tantrums in the general mindset is really important. The 'tantrum' conflation we have around meltdowns is one of the reasons why autistic people experiencing meltdown are routinely injured or killed through overly rough intervention.
It's a total misunderstanding of what is actually happening, why the autistic person is acting in this way, and inadequate intervention kills. Look at Oliver McGowan, who died when doctors gave him anti-psychotics he was allergic too rather than properly deal with his distress.
Encouraging people to shift their language is an important step alongside pushing for education, acknowledgement, and justice. Even people most educated in this, including other autistics, are prone to slipping back into a mindset if it's enforced by the cultural narrative.
There are so many routes and factors in improving things, and many of us who are asking for specific language change are also working in other areas as well. They all fit together.