As an aside, calling an idea complete bullshit based on an nitpick is pretty weak, especially since you're wrong: when tgv started in September 1981, they only had part of the line constructed. Without compatibility, I.e. a completely dedicated system, you could've only traveled between two random towns.
It means the exact same fucking thing in every context. Dedicated means infrastructure which exists solely for high-speed train, not that high-speed trains can only exist on the dedicated infrastructure.
> It would mean complete incompatibility
That's completely nonsensical. European high-speed lines are dedicated, non-high-speed trains do not run on them, it's the high-speed rolling stock which is compatible with older electrified rail lines because they use a standard gauge and compatible/switchable electrical feed (some of the more complex rolling stock having to cross multiple borders can handle 4 different power inputs).
> This is not what EU high speed rail was built on, they use a lot of legacy lines
And they use dedicated infrastructure and have done so from the start.
> As an aside, calling an idea complete bullshit based on an nitpick is pretty weak
It's not a nitpick to point out that your statement is factually entirely incorrect.
> especially since you're wrong: when tgv started in September 1981, they only had part of the line constructed.
That was still a dedicated right-of-way which it started with, putting the lie to your statement.
> Without compatibility
That has nothing to do with your original statement. Your statement was not that high-speed rolling stock should be compatible with legacy rail and able to use it. Your statement was that european high-speed rail "definitely didn't start" with "dedicated rights of way", and further that high-speed rail only have some dedicated rights of way.
Yes they are standard gauge and can run on regular old rail and that's plenty useful, but no that's not what they were built for, it would be a complete waste of the rolling stock.