Agree, the BoL does not implement the 10-turn spell effect that is in the description. Without that, the item is not particularly special, although the 6m light effect can be situationally useful. Most fights only last a few rounds, so the 10-round effect is generally not needed, but would be very helpful occasionally.
Unfortunately, once-per-long rest features are effectively once-per-fight for players that simply spam long rest after every fight. That's a flaw in the D&D rules that has been present since the 1970s, which can only really be resolved by DMs abusing the rules to encourage players to take less long rests.
It could be that the legendary items have been nerfed to avoid this problem, but the description has not been updated. A better solution would be to manage the short/long rests better, so that ( for example ) you can have a single short rest after a fight, and a long rest after one or more fights following your last short rest. This would result in a minimum of 3 fights between long rests.
Alternatively, it may just be an implementation bug; I'd need to compare with other legendary items as I find them.
