Designing Question

I was working on a game that I've been putting a lot of effort into. I've ran into a problem and a question that may

make or break the system from my JRPG

I have two mechanics I added to the current project:

The ability to change your class while on the field but, not while in battle. You can also add a sub class but, getting into that would be getting of topic.

There's also the ability to add permanent skill via "Skill Trees" to which ever character you want to develop, adding buffers to the healing class as well; So if you where working on the healing class, You could later equip it as a Sub-class and have some pretty good heal ability if your ever put into a situation where you have little heath, Healer's down and no items left. When your outside the big battle getting ready for said battle. Your equipped weapon won't be enough to protect you when working on it. The skills you lean for the "Skill trees" will very to each charterer. Giving them there own little in graved skills that forces the player to think out who they want in the party and not to just change up there jobs of there favorites to fit the problem at hand. 

Now knowing all this,

Here's my question:

Is the "Skill tree" really necessary?

The player could grind up the fighting class and just equip that as their sub-class so they have those skills to protect themselves or have there party members protect them; kind of making the skill tree use-less in that case. On the other hand if I take that out, that would interfere with skill strategy layer of the game and would turn if into a Final Fantasy 13 clone. (sorta) 

I'm the worst judge of my game in this case, I need help deciding this big part or my game! >_<

I actually got an idea from reading this

(By the way, taking out the the skill tree)

The idea was to give each charterer their own class set like you said. Give them there own unique strengths and weakness Like:

The main physical attacker classes will be about attack and the idea of "Attack, ask questions later"

The main healer classes will be about healing and some strong light spell attacks for when put in a pinch and  the revolves around idea of "Keep the party alive and going"

and the balance party member classes will be able to do both types of skill but, won't be better the the characters that major in the skills/class but, will still be very useful.

How does that sound?