19 hours is where I expect a Japanese RPG to 'start'. Definitely not for me.

I pick a random jrpg and I play it to finish. During my time:

I enjoy the story of the  of game.

I enjoy the characters.

Phenomenal music

Attractive art direction

Fun engaging battle system

Good amount of side quest/Post game content

Satisfactory ending leaves me fulfilled.

I look at my end time and its 26 hours. Why does it matter if I was delivered a enjoyable game? Why does not being 40+/60+/100+ even matter? Why is a arbitrary number even thing?    

Well, Till the End of Time would have been a much better game if it was only 20 hours. That way the plot wouldn't have been ruined by "you know which twist".

Okay so side quests are standard fetch, and kill quests. There is also a bonus dungeon.

Agreed good length. My ideal length is 25-30 this is just under that so not bad.

It's a traditional JRPG. Most games like that take 20hrs unless there's a big budget involved. FFXV is said to be 40-50 hours and that's a big budget title.

20 hours for an amazing game is a perfect length to me, even though I know that's short for a JRPG. Even 5-10 hours is too long if the game is horrible. If a game captivates me from the start, it's well worth the 60 dollar investment and shorter length.

I'm not sure I understand the notion that a game has to be a certain length to be worth the price tag.

Honestly, if it is ~20 hours long, I'm more likely to buy it. I already have 3-4 games that I'll probably spend 60+ hours on during the Summer and Fall, so SO5 being possibly 20 hours long is good thing for me personally.

If you compare a person's experience that throughly played a game to the experience of someone who only beat the main story arc, it's almost like two different games were played.  It's not really an arbitrary number as you put it. How do we measure content in a rpg or any game? How else is someone to really know if they just skimmed the surface of a game versus throughly playing it for all it's worth? Those things are not that easy to define but max playtime and average playtime will give ya a clearer picture of what to expect content-wise.

If a dev tells gamers that their game should take 30 hours to beat on average, you'll have an idea how much content (main story, side quests, crafting) there is for you to do. Anyway, I highly doubt that 20 hours is the normal playtime for Star Ocean 5. It's probably in the 40s to 100s.

He also revealed the amount of planets you visit. 

I dunno how to do a spoiler tag so if you work out this math question you'll know

5 + 10 - 3 - 5 + 4 - 10 = the amount of planets you visit