Helium exists, it's called NBLE (Noble), which I consider to be all the Noble gases in one element.
HELM is NBLE. NBLE represents all the noble gasses because each noble gas on its own is boring. NBLE turning into PLSM when sparked is actually to mimic neon signs, though you'd need good insulation to contain it. All of the elements you suggested have one singular sentence boasting its use. An element needs to be more useful than "Biological reactions and an element we already have (ACID)" or "A good poison (We have a thousand of these)"
TTNG would be interesting but I'd make GAS have a ctype (similar to LAVA). The problem is that it breaks old saves.
Tbh, the fusion chain in TPT is long enough as it is and we don't need to extend it just for the sake of "realism". It's a lot harder to add an element from real life and attach uses than it is to think of a problem that most people share, prove that it's not possible (or extremely impractical) to solve it with base TPT, solve it with an element, and then give it a name and color.
It's not too much for code, in fact you can mod all these in if you want. It just doesn't fit in vanilla TPT.