that's assuming that 8 always = paint. If we treat it like a letter in the alphabet, though, it's only the base sound that counts. 'a' isn't always 'ay,' 'b' isn't always 'bee,' 'c' isn't alwaus 'see,' etcetera. 8 can be 'ei' 'ay' or 'ai' as long as it makes the same sound as the beginning of the pronunciation of 'eight.' That's why it looks alright at first glance, because we read it like a letter.
'b' is not 'bee' when it's used in words. Basket Ball. Two 'b's, but no 'bee' sound. Also, agression, you ignored what I said about ommiting the ending sounds, like we do with other letters. 8 is pronounced 'ate' but if you were to use it like a letter, you can omit the 't' sound. Your examples still included the 't' at the end of 'eight'. It's like the letter "H" which ends in a 'ch' when pronounced by itself, but we never pronounce that part in a word that doesn't end in 'ch.' Similarly, if '8' occurs at the end of a word, you DO pronounce the t. Example: h8, sk8, infl8, L8. Then you can add suffexes that don't effect the pronunciation of '8,' like h8er, sk8er, infl8er, l8er.
P8 is not a word, but P8NT could easily pass for one, if we treat numbers the same as letters.
But still, who cares! Why cant we just spell it Paint! Its not like spelling is p8 or p8nt saves us any time. It just makes us look more illiterate. Like those kids who go "Yo waz ^ dawg? Im gnna go sk8 nw, yaz wanna com?" Trust me, Ive seen people that talk like that.