Fair points. It's all guesses about the unforeseeable future, but I would estimate that a multigenerational ship is in arm's each if we really wanted to, whereas accelerating so much as an orbiter (let alone a lander, or a whole rover, or a live person) to 0.9c probably requires a tech level we don't have due to the fuel requirement for deceleration. Maybe a fly-by could work, then burst back the results with some enormous amount of energy, but that's a lot of cost for very little information.
When making a generational ship, for safety we'd still want to do years of testing on orbit to see whether a chosen ecological system really does form a closed loop. Water recycling on the ISS is 98% efficient according to NASA, so with refuelings from ice moons every couple decades (solar system hopping) that should be covered. Ion engines are apparently also a thing (still sounds like science fiction to me, but they've been in production on space missions for a long time apparently!), I don't know what kind of longevity those have though, or whether refueling is realistic (might requires landers with expansive equipment for refinement of elements). Things like floor space, the way that I see it, that's a matter of cost more than a matter of ability, so having enough privacy so you don't kill each other is within our current tech level – again, iff we'd really care to do this. Hence I'd say we can do this nearly today, and then it also doesn't matter much if you need 400 years for 4ly or 12'400 years for 124ly.
On the other hand, by 10k years from now, I would think we can make a 0.9c human-sustaining craft, so maybe you're right that we'd rather choose to wait a thousand years and see where things stand then rather than putting effort into launching a generational ship next century, whereas with a 4ly target the generational ship is much more likely to be faster. Maybe you're right that this distance difference does matter. Not for ability so much as for psychological "would we spend that effort given the perspectives" reasons
