different aircraft for different jobs.
usage of the 18 and A-6 has been covered already - suffice to say
the 18 is also limited by range issues, even with inflight or buddy
refuleing.
the a-6 is an attack aircraft that needs to work as part of a
combined group for it to be successful.
the F-111 was being used in its original secondary role [primary
iirc was tactical nuclear strike before stand-off tactical nuclear
strike missiles became possible] as a tactical strike bomber - ie.
get in quick, bomb with conventional [albeit laser guided]
ordnance, get out quick.
stealth - again its been covered already, but an all stealth range
aircraft isnt going to work.
for a start stealth properties, in the way that they are
implemented now are near useless for conventional air-to-air [the
F-117 is known as an inherently [fairly] unstable aircraft,
sometimes a good thing in combat, but not for this design]
the atf/advanced fighter projects in the us are going some way to
address this problem, but as covered earlier military doctrine goes
with the aforementioned strike pattern.
the b1 has ongoing issues, with design/production flaws, that
leaves the fleet in [considerably less than the 100 that were
originally produced] grounded alot of the time.
[the last mass grounding iirc was due to cracks appearing in the
airframe around the wing roots..]
when was the last b-1 you saw going up on a sortie compared to the
50-year-old-design b-52s?
f-111's are now retired anyway, with their role having been filled
by... ...?
i guess a combination of multi-role capable aircarft..