Bear/Buff are outdated trucks, essentially remaining operational due to the amount of logistics hardware already existing in those airforces, making them stretch their lives as far as out as possible.
Blackjack/Bone, on the other hand, provide niche capabilities, that although in 80/90s would've been sought after, they are still vulnerable in highly contested environment.
Stealth is the only way to go in the coming years.
It is inevitable that an "all stealth" fleet of combat aircraft will emerge in the future for high intensity missions, ranging from strategic bombers to heavy weight and medium weight fighters and UAVs/UCAVs.
But that is quite far into the future and the money for an "all stealth" fleet simply is not there yet for most nations, and for bomber aircraft, non-stealthy aircraft are still able to carry respectable payloads including longer range stand off payloads that can make their effects felt even if the deployment aircraft remain inside their national airspace.
In relation to the H-6s, the H-6K/J/N family are a mature, relatively affordable regional bomber capable of carrying a decent amount of weapons (6 large ALCMs or the equivalent weight in AShMs), and with capacity to integrate future new payloads as they are developed without having to consider the restrictions of an internal weapons bay.
Even in a high intensity war, the sheer number of H-6Ks and the number of KD-20s they are able to collectively carry and the range of the KD-20s means even without exiting Chinese airspace they are able to place significant targets in the region at risk.
For the purpose of being a regional bomber stopgap before proper stealthy longer range bombers emerge, the H-6K/J/N family are perfectly fine and are going to be with us for some time into the future, because at the end of the day those H-6K/J/Ns are still better than no bomber.