Were you playing on the lowest difficulty? Because most of the bosses died way toó fast. Case in point, Aeshi Nero(Second boss) isn't supposed to last 15 seconds
On normal, the black UFO became an trouble when I was sweated my a_s off from trying to juking directions to dodging their bullet, like playing an Touhou game. (3 UFO in same time) I prayed the heavel of the tanks and shields rebels can shoot them down or tanking bullets for me.
Can i ask what difficulty your playing on? Because although the rest of your gameplay is flawless yr boss battles seem way too short for comfort, if you were playing on a neo geo mame system (proper arcade machine on level 8, your boss battles would be way longer than what they are on this playthrough