The waters certainly aren't clear; but I think it still makes a good point to those that argue there is absolutely zero obligation to people marginalized for historical reasons. As I'm arguing elsewhere, "obligation to" doesn't just mean giving money or land; but doing things like helping to remove systemic barriers, ensuring access to opportunities so that for generations entire communities and cultures are on better ground, etc.
Your points are fair although, for me at least, the obligation is not based on historical injustice, but on an obligation to help improve society in the present. A historic obligation seems to me to suggest this exists independently of current need.
In England, people with Norman family names are wealthier than people with 'Anglo-Saxon' family names. This is the legacy of conquest and historical injustice, but few people think there is any obligation or need to redress this group inequality. It also shows the longevity of historical disadvantage that can't be easily remedied even once there are no systemic barriers left.
Most disadvantaged communities can point to some historical injustices that can partially explain present disadvantage so we end up judging certain people as being less deserving of assistance than others for fairly arbitrary reasons which leads to bitterness and hostility.
Also, when the aim is to redress group inequality, it tends to benefit the already privileged members of the group rather than those who most need it. Trying to remove vague, systemic barriers with crude bureaucratic methods is not always particularly effective as principle is easier than effective policy.
imo at least, if the obligation thus stems from present need rather than historical injustice, then better to focus on the present need. This doesn't necessitate a one size fits all approach of course, and attempts to improve Native American communities may differ from those to improve rural Appalachian ones.