layman here. i understand that if said theoretical computer did exist, encrypted stored data using today's standards is for the most part compromised, outside of further obfuscation, which the popular opinion seems to believe only helps so much.

that means the past is compromised, with some amount of implementation afterwards. i've always wondered just how much the future is compromised.

i've always thought about encryption this way:

  P = some degree of computational power
  
  A = some small unit of P, like a laptop
  B = the largest unit of P practically
    possible under the same laws of physics as A

  (data encrypted by A cannot be "cracked" by B in a reasonable amount of time)

so in my head, so long as a normal civilian can access qubit technology (likely questionable), encryption still works by increasing the number of rounds. what am i missing?

edited for format, then again for clarity