A lot of RPGs have MUTE characters. Ys, for instance. Lunar 1's Alex is almost mute, but he has 1 vocal line in the game I think.
True, but other player characters in Lunar have lines, and tons of them (Ramus, Luna, Nash, Mia, Jessica, Kyle). Ys, however, is difficult to consider an RPG considering there is no player character development and the story isn't about Adol but about the world of Ys. Besides, the "mute" criteria is a minor one...it can be overshadowed by strong character development, which is the case in Lunar. Alex has one single spoken line in the Sega CD version and several lines in the Playstation remake, but the focus on the characters in Lunar is so powerful that it doesn't matter if Alex barely speaks.
Also, it's important to understand that a lot of games that are labeled as RPGs are not actually RPGs.
What if there was a game that had all of the mechanics of an RPG. Let's say it was exactly like Phantasy Star 1. But there was no real story. The dialog just consisted of "There are more monsters here" or "There is a boss monster at the end of this dungeon". The only thing changed is what the text says. Is it still and RPG?
No. It loses its RPG title and is demoted to a simple adventure game or even a "mob game", which are certainly not RPGs in any sense of the word. The gameplay style doesn't make the game an RPG or not.
To me, games like Exile are most certainly NOT RPGs. Exile 1 can be beaten in less than 2 hours and features extremely weak character development.
Exile has far more character development than Ys. Far more. The time it takes to complete is irrelevant. Furthermore, Exile and Exile II both focus on the main characters of the story. Ys focuses on the world around the main character and not the character himself.