@OP: The short general answer to your question is “yes, it will always be this easy to avoid interdiction.”
Now some clarifications and caveats:
• The difficulty of beating the interdiction mini-game will always remain about the same (super easy as youve noticed), even as you go up in rank, take on more advanced missions, carry more valuable cargo, enter more “dangerous” systems, are interdicted by more elite pirates, etc.
• The type of ship you’re flying does have some impact on supercruise flight characteristics, and hence has some impact on how easy it is to win the interdiction minigame. But the differences are negligible IMHO, at least with the baseline of difficulty already being so low to begin with.
• The Interdiction minigame
used to be much much harder to win, and the difficulty was much more varied, until one day Frontier patched it to be as easy as it is now. There’s always the possibility that a future patch might make the interdictions challenging again, although I personally doubt this will ever happen.
• In a PVP situation vs another human interdictor, all bets are off and none of the above applies.
TL;DR: Interdictions are a bit of vestigal gameplay from an earlier era of Elite, and are more or less a formality now. You will never be involuntarily pulled out of supercruise to engage with a pirate that you dont want to engage with, unless you’re asleep at the wheel. None of this changes as you advance through the game.