With that premise, that could very well be.
Thanks for conceding that.
The whole double-spending scenario is proportional to bitcoin value. If value were to go up orders of magnitude, the number of blocks needed to get your investment back goes down the same order of magnitude.
But difficulty, and therefore cost of a double spend attack, is also proportional to bitcoin value, so the rise in the potential reward of a double spend attack, is canceled out by the rise in cost in pulling it off, as bitcoin value increases.