I have the game, played 80h and I understand Op's frustration as I felt the same till I learned how to play.
OP, the game is easy AF when you know how it works.
Do this against bosses:
Spam melee + Side dodge to cancel combo (like 3 melees, dodge, 3 melees dodge, depending on the character add more melees). If you do it correctly and have the correct skills equipped you could even deplete the stun bar of the enemy leaving him incapable of moving and receibing x2 damage (also is how you activate cool cinematic super attacks).
ALL bosses of this game have a super telegraphed move that is like a circle aoe around them that breaks your defense and stuns you. Stop doing ANYTHING and spam dodge forward as crazy. A thing that the game never tells you is that if you use your defensive move (hold defense and press Square on PS4 I think) at the same moment they do that attack you won't get any damage or stun (and you can spam it so you don't have to exactly guess when the hit is coming, just spam it like 3 times and 100% sure you will dodge it).
ALL bosses of this game have a moment when the camera makes a closeup on their faces and they jump to the other side of the planet and start spamming Ki blast, Ki attacks, etc. Just keep your distance and DODGE. Just dodge. Use this time to use restoration items, senzu beans or even to recharge your ki. Most of the times when that attack ends the boss will be "tired" for some seconds, THAT'S when you charge your "limit break" bar and start spamming melee as crazy and after every combo you add your strongest ki blast.
ALL bosses of this game have a phase when their body shines, or is covered by an aura and start rushing towards you. DODGE, DODGE DODGE like crazy and abuse of the super defense skill I told you before. It makes you virtually untouchable as long as you have ki. Usually the boss will get tired after that so it's your moment to use your limit break bar and go for melee spam and ki blasts.
It's a game that punishes being greedy and not knowing ALL BOSSES have this patterns. There are specific phases for you to spam melee and there are specific phases for you to forget about dealing damage and just dodge dodge and dodge. The AI of the game is retarded so it's totally exploitable.
After learning that I started to enjoy the game a lot. I started stunning bosses making the battles super anime-like.
Another tip: Have ALWAYS equiped on all your characters at least 1 melee super that has in the description that deals huge stun damage. That is your melee combo finisher. Your main goal is to deplete that bar as much as you can before the boss goes into one of his inmortal phases.
EDIT: I never grinded while playing this game. Never grind. The game auto levels up your character after each important story moment so grinding is pointless. Just get a bunch of healing and Ki recovering items.
I just beat Android 20, who obviously started spamming energy absorbing moves near the end of the fight, recovering like two health bars
Well...dodge and don't use ki blast. Also this happens in the manga so you should expect that to happen ingame :3
As the guide said: "Spam melee, Just keep your distance when he glows red, dodge, kiblast his face after dodging his kiblast with a sidestep".
now 18, who spams unavoidable energy blasts near the end of the fights, and instakills me? Or spamming stunning moves and kicks the hell out of me while I can't move?
She is a kiblast spammer. Keep your distance and dodge to a side. When she gets his "anime closeup" moment you know she will do the move 3 times. After the 3rd one big bang her face. When she starts spamming her "let's go!" attack dodge backwards or exploit the ki defense attack and then melee her ass.
All the bosses have their patterns and their gimmicks. This is not a Naruto Storm Game or a Tenkaichi, they intended to do an Action RPG with boss patterns and strategy for each one. Spamming ki attacks or melee brainlessly will only end on your death against bosses. You can do all the spam in open world bosses tho.