The point @conordeegan is making is that there is a large opportunity space, currently unexplored in both hardware architectures and algorithmic improvements, for quantum computers capable of attacking private keys.
Small shifts in architecture, error correction, qubit networking, memory, etc., all present massive shifts in the threat model timeframes and resource needs.
That makes the threat more existential because it is rapidly shifting and includes many unknowns (due to secrecy among potential attackers and, more importantly, yet-to-be-discovered improvements in quantum tech).
