KB, yes like most trainers, they can weaponise it. When was the last time a decent air force sent a trainer to war?
Isn't the Hawk a trainer? I know there are weaponized versions of the Hawk. Have they never gone to war? Not even for the Indian Air Force? I think IAF is a pretty "decent" air force. And Indonesia has certainly used their Hawks in combat. The also have F-16s. Does that qualify them as a "decent" air force?
And for decades the F-5 (also a trainer) was a front-line fighter for many nations, with more than a few seeing combat.
And the A-4 was also a trainer and was used very extensively in combat in Vietnam and in and around Israel. Not to mention the Maldives (oops, Falklands). ;-) I think USN has a pretty "decent" air force.
The A-37 was used extensively in combat in Vietnam, South America, and elsewhere. And USAF is a pretty "decent" Air Force.
So I believe there's a long history of using jet trainers as fighters.