Traditionally the aircraft is the unpredictable manouvering defence penetrator that delivers the weapon to a release point and then vacates the area on to the next target.
New weapons, either flying very low and hard to detect, or very high and just to fast to intercept reliably do a better job of evading enemy air defences than the very large aircraft that carry them.
Defending against 200 PAK DAs or 200 B-2s trying to enter your airspace and drop a nuclear bomb on target means 200 targets to engage.
If those aircraft carry long range hypersonic or stealthy missiles then the problem is multiplied, and with extended range the need for the aircraft to expose itself to enemy fire diminishes to the point where it is not worth exposing your aircraft to enemy air defences to launch attacks.
Obviously when the enemy are ISIS an at that state are not getting air protection from the democratic peace loving west then Iron bombs can do the job cheaply and effectively, but if the expected problem might include US fighters or Turkish fighter offering air defence then sneaking in a few low flying cruise missiles makes sense instead to avoid confrontation and yet still take down those terrorist targets.
When America is the problem, or a group of American ships then low flying stealthy and high flying hypersonic make a good attack combination if you can time it so the stealthy missiles arrive first and make the ships focus on the wrong direction and down low, then attacks from up high at very high speed become even more shocking and effective.... against any navy on the planet... no matter who is supporting or funding them.
A subsonic bomber is cheaper because less energy is used to fly it around, so PAK DA will likely be cheaper to operate than the Tu-160 and the Tu-22M3, but should be stealthier than the Bears.
Having said that their Bears and Backfires still have plenty of hours left and could be used in a range of roles with lots of potential... I mean if their PAK DA and Tu-160 are getting air to air missile capability imagine a Tu-22M3M version with its Mach 2 capacity but also an enormous nose mounted AESA radar and 24 tons of air to air missiles patrolling the far east and far north...