Specifically, why would some say that the time experienced for those on Earth would be far greater than the time for light to travel to the destination and back. Example, I have heard it said that if you travel to Alpha Centauri and back at the speed of light, far more than 10 years will have passed on Earth than what it takes for light to travel there and back.
Here is my thinking on this when considering the speed of light time dilation versus actual distance traveled. The speed at which I am traveling at means that I experience time far slower. So if I were to adjust my space ship's experienced travel time to compensate for this time dilation, then I could experience travel to say Alpha Centauri in seconds for me. Even though the actual time it took, relative to Earth, would be about 4.5 years.
If that is the case, then all of these concerns about travelling at relativistic speeds should theoretically be moot. Yes, that means in a round trip to and from Alpha Centauri for the study of the stellar system it would take almost 10 years to those on Earth. But for those on the flight, it should take what I would think is seconds plus time spent in the system doing the study.
All the arguments I see center around the idea of traveling those distances over the duration of time as experienced by the traveler. Thus, when I hear people such as Neal DeGrasse Tyson talking about traveling 4.5 light-years, it always sounds like he is saying that the traveler experiences the passage of time as 4.5 years while moving at relativistic speeds. Thus the problem for the traveler is that going there and coming back while experiencing those years means far more time has passed here on Earth.
But if you are traveling at those speeds and those speeds slow the passage of time from your perspective, then you shouldn't be traveling for 4.5 years from your perspective because you would severely overshoot your target. Instead, you should calculate how much time would pass from your perspective in order to travel 4.5 light-years, which I imagine would be experienced in seconds or possibly minutes. Then travel for that long from your perspective to reach your target area.
Is that correct or am I fundamentally missing something about time dilation and traveling at relativistic speeds?