Let's not confuse Destiny with simple predetermination, shall we? The six Matoran who left Metru Nui for Voya Nui did so because they had to take action- the very life of the Great Spirit was at stake. Collectively, they each made a choice to leave for places unknown with a team of five other Matoran (and Takanuva), each from another Koro, each leaving behind what would've been a pretty prominent role in the rebuilt City of Legends. "Rebellion" is the operative word for BIONICLE in 2006, and the departure of the soon-to-be Toa Inika in defiance of their Turaga's orders is but one of many examples. The Piraka rebell against the Dark Hunters. The Voya Nui Resistance Team rebell against the Piraka. Brutaka rebells against Axonn's friendship and better judgement and against the whole of the Order of Mata Nui. But the biggest rebellion of all is the root cause of all these smaller games of cloak-and-dagger: The Plan. All of 2006 through 2008 is the but the motions of the cogs of The Makuta's machinations- manipulation and circumvention of that pre-programming that you mentioned to ensure his ascension to what is basically Godhood, all while keeping even his closest allies in the dark until the very end.
The Toa had to be paragons of virtue the whole way, or else... well, you can see the canon AUs for yourself. Toa Empire is what happens when our beloved elemental knights go too templar and establish a police state. The Kingdom isn't entirely terrible, but it's surely not the best ending. Matoro suffers in silence and Spherus Magna stays unreformed forever. An incomplete conclusion. In the end of the main story though, the Toa triumph, and even with their victory stolen by Makuta, Mata Nui himself honors their many sacrifices and finishes the job himself, all while under the mantle of 'Toa'.
The word 'Toa' means more than just 'Hero'. It's a term reserved for those who doggedly pursue justice with their whole being, those who stand in defense of those who can but barely protect themselves. It's for those who stand in the face of impossible odds and give of themselves to the point of ultimate sacrifice- never for the sake of personal honor or glory, but for knowing they've made the Universe a better, brighter, safer place. That's what it means to be a 'Toa'. Mak-u-hero all you want, but at the end of the day I'd much rather have a Lhikan, Kopaka, or Kongu in my corner than a Stormer, Rocka, or Furno.