It wouldn't be inconsistent, certainly.
I prefer that we blame the game for stupidity.
Jyscal was sent, was he not? But as he still had something to do, he was (with great effort), able to leave for approximately five minutes. Notice the effect he had on other unsents, namely Auron. It's clear that the Farplane was trying to bring him back within an AoE. Shuyin is one of those weird Unsents, though. I would still prefer to blame X-2 for stupidity.
Or they were horribly scattered throughout Spira by the Spherimorph, or they could have been lost, or they could have been brought there through natural means. We don't know the topography of Spira as it was 1000 years ago. The mountains could have formed in that time.
Imagine the One Ring. From 3441 SA to 3019 TA, it went from Mordor, to Minas Anor, to the Fields of Gladden. From there, it escaped, went into the river, and was picked up by Gollum, who moved into the Ered Mithrin. It escaped once again, and went to the Shire. Then it went back to Orodruin, and died. Yes, died. There's no reason a similar journey could not have taken place for the sphere.
The Calm Lands is only used for the Final Aeon fights. In context of the war, the game makes it seem as though Bevelle was pushing on Zanarkand and broke the city defenses (Gagazet). There's no reason for Zanarkand to leave the safety of their mountains.
In the final battle, I believe that they only used summoners, their last resort. He seems to have no knowledge of the act of summoning itself, even if he knows what it is. He could have been killed as a citizen, or in a previous battle, but I doubt this.
Seymour explicitly said that it was a recreation, not a representation.
But Zanarkand was also huge. Imagine New York city. Diversity + space + time. Tidus seemed to be shocked by it, but I'm not sure whether or not he actually thought he was there again (he's come up with stupider theories, such as travel through time), or because Seymour was hitting on Yuna.