I can get why some might dislike it even if I don't (I see it as a nice option for a seasonal jumper without it being specifically a Christmas one), but personally, I think pushing meltdown or overload to be a ND-only term falls too much into the social shift where people's distress is ignored without a diagnosis, and even then it's often not enough so there is sometimes a push for more diagnosis until we've 'enough' to be taken seriously. NT people can get overloaded or 'meltdown' - there is research on it particularly in relation to during and after trauma and as emotional vocabulary, it's a useful term, just like anxious doesn't always mean medical anxiety but can just mean really nervous or just those physical sensations while still processing the feeling.
so now, the neurodiverse community have no language that expresses the biological phenomena that they actually experience during a “meltdown”
I've always used overloaded - because that's what it feels like physically to me, that my senses are too overloaded for my brain to process. If it's sudden, I might use set off. Those might be an Americanism or just older language though, as that was the language used by professionals helping me when I was a kid. I've only heard meltdown used in that way in the last decade or so (and at first more by parents than ND people). I actually don't really 'get' the meltdown as a metaphor for what's going on for me.
Toddlers having "tantrums" are also often overloaded as they're still building their capacity to process. Same with teenagers as they rebuild. I've use that language as I was taught with my kids, whether they're ND or NT. I thought it followed the whole 'vital for some, valuable for all' concept that is often an important part of inclusive activism.