just because someone shows you something or does something doesn't make it right or the "rule", you seem to be the impressionable type. rather than take the word of a few adults and just go by that educate yourself. If you took the time to search "timing" in tech you would see that the average advanced timing is 14 degrees. It is also possible on pump gas to go up 16 + degrees on some motors w/o issues, again these motors are well known on many stang forums, clubs and strips to respond to timing well.
I'll make this short since there is tons of info on this very subject,
education..The initial timing specs from the factory are conservative. To optain maximum engine performance from the stock 5.0. an inintial spark setting of 14 degrees is recommended, with the OE EEC-IV computer this comes out around 38 degrees advanced. AOD cars like a little less advanced spark. THe 1986 fastburn combustion chamber design requires less advanced spark timing and a mass air car using the 86 fastburn heads is limited to a maximum of 14 degrees. High compression motors, superchargers, turbos and nitrous also need less advanced spark timing. this info is from both text and online searching.
If you took the time you would also know that for optimum street performance you would advance the timing 2 degrees at a time accelerate under load then back it off once you get pinging this could be at 12-16 or more depends but to tell some one 16 or 17 is wrong makes you wrong.
If you are at the track and you want play with your timing you do the same thing but keep advancing until your times slow down then back it down until you dial in, this could be in a range from 14 up to 18 degrees. again this is in both text and online.
If you want to listen to those guys that is fine but if post it and push it onto others you are going to get guys who might think otherwise and just might know a thing or two. Don't believe everything you hear and be willing to learn before you argue.