I have just reread the introduction part of the Abridged P6 codex, an implementation of E6 rules for Pathfinder. And I noticed (once again) a very interesting passage:
One way of envisioning the character levels is that a 1st level character is roughly equivalent to a journeyman craftsman – a squire just completing their training, a conscripted farmer just off their first tour of duty, or a wizard just finishing their apprenticeship. A 3 rd level character is roughly equivalent to a master craftsman – well above the peasants, common laborers, and even craftsmen in most rural villages, but not uncommon in the towns and cities. Fifth level would include the renowned master craftsman – one who has achieved a rare height for their profession; they would only be found haphazardly in anything smaller than a city and be few in number for any given profession even in a larger city. Beyond 6th level, a character or NPC would be truly epic, the type about whom legends will be spun unless they work hard to hush them up.
While I understand clearly why is it good to go no further than level 6 (because 4th level spells), my question is:
Why does this game not stop earlier, for example, at 3d or 4th level?
It would probably be kind of unreasonable to permanently stick with a situation where everyone has "just finished their apprenticeship", but being "roughly equivalent to a master craftsman" is already a pretty high position. Not everyone should be "truly epic", achieving the potential of standard Pathfinder level 8 heroes.
I am seeking for answers naming exact disadvantages of low-level play (levels from 1 to 5) compared to level 6 play, not general rant. I also ask to adhere to Good Subjective, Bad Subjective guidelines and support your answer with actual experience.