You don't seem to understand the reason Neo is large star level. Neo is
at the top of the universal food chai, and as such is stronger than
Cosmos Mammoth's and the
Demon King. Cosmos Mammoth's are "... gourmet elephants with heads as large as the sun
("õ©Ç Úá¡ÒüîÕñ¬ÚÖ¢þ¿ïÒü«ÕñºÒüìÒüòÒü«þ¥ÄÕæ│Òü¬Þ▒í"), and the
Demon King is
much larger than a star. Also Neo used an attack which could
completely wipe out the su.
That is why Neo is large star level. You also don't understand the concept of
attack potency.
"A character with a certain degree of attack potency does not necessarily need to cause destructive feats on that level, but can cause damage to characters that can withstand such forces."
Don Slime could possibly only have small star level destructive capacity, but regardless he fought
Neo Acacia for an entended period of time so his
attack potency would be large star level.