Re: Through a Lens, darkly...
Not even a Lens protects you forever.
IIRC, there were 'dark' lenses appearing by the time of "Children of the Lens", so even the Lens was reverse engineered.
The Arisians always knew from their 'Vision of the Cosmic All' that they were not the ultimate lifeform. That is why they force-evolved and then passed the mantle on to the Kinnision clan.