Are strategic bombers still useful, or are fighters taking over this role?
The reason that small aircraft are used in the bombing role is flexibility and cost. If you load up a B-52, it can only be in one place at one time, travel at subsonic speeds, and be expensive to operate, risking more crew and equipment. Using smaller attack jets allows reaching targets across a wider geographical area faster. And while past conflicts saw massive bombing campaigns that favored the use of large bombers, more recent conflicts have seen much less of this tactic. Smaller, more targeted strikes are more typical, where a large bomber would be overkill.

Take a look at the cost per flight hour for various aircraft. A B-52 will cost \$70,000 per hour to operate, and a B-1B \$60,000. Compare this to an F-16C for \$23,000 or an F-15C for \$42,000. The A-10 costs \$18,000. For stealth, the costs go up to \$170,000 for a B-2 and \$70,000 for an F-22. So why send a B-52, when a few F-16's would cost the same amount? The fighters will also be able to defend themselves, and still be able to carry out a mission if an aircraft drops out. The same argument can be made for the stealthy class.

Strategic bombers still have their uses, but the bomber role is much less demanding than the fighter role. With proper maintenance and multiple equipment upgrades, old bombers can still fly bombs to their targets just fine. Fighter jets have much more complicated requirements, such as stealth, speed, and maneuverability, where advances in technology will justify the costs of continued development of new designs.

Aircraft are becoming more generalized because it is more efficient. In some areas such as naval aviation, this is even more critical. Why have separate planes for electronic warfare, attack, and air defense? You would be limited to a certain number of each type, with little or no cross capability. But with more generalized aircraft, you can have more aircraft with a certain capability across the fleet. If a certain capability becomes less important, you don't end up with a whole group of aircraft becoming useless. Aircraft can fulfill multiple roles in a single mission or deployment.