First thing is that you need to realize is that lock on isn't optional in DMC, it's mandatory. That means during combat, the R1 button has to be pressed all the time. When you remember to do this, then you realize that the moves in the game are actually easy to execute. Streak? Forward and Triangle. High Roller? Back and Triangle (hold to rise). The moves are all a combination of back and forward. After that you have to realize that dodging or evading is all a function of the Jump button and even a regular jump has invincible frames to get you out of trouble. Since you are always locked on, when you press the jump button you will generally evade the attack as long as you timed it reasonably well. The only time you shouldn't be locked on is if you want to do the Breaker moves, so just let go of R1 briefly and press O then back to holding down Lock on. This is just a basic learning curve thing with the DMC games, nothing compared to something like Souls games where it's a completely different system altogether from other games (and even more obtuse). All the moves are listed in the Skill lists in the options section. Definitely get into an open space and execute all the moves available in the demo to get a feel for them. By DMC standards, this demo and the boss were pretty easy, DMC1 was the original "git gud" 3D action game before all these Souls, Monster Hunter, Ninja Gaiden, Bayonetta etc. type games. But remember how many times you died against bosses in a Soul game or in a Ninja Gaiden, but you learned and overcame it... this is no different. New system, new controls, new game, new mindset.
Yes it IS different and they aren't really comparable but that's exactly what people do. Like when you see people come into DMC and say "there are only 2 combos in the game I feel so limited compared to so and so" you already know what mindset they are approaching this from.