Making an object jump (without rigidbodies), while using enum + gravity

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class Player : MonoBehaviour
 {
     private float groundSpeed = 0;
     public float jumpSpeed;
     private float speed;
 
     public float gravity;
     private float baseline;
 
     private State playerState;
 
     Vector3 moveDirection;
 
     enum State 
     {
         onGround,
         jumping
     };
 
     void Start()
     {
         playerState = State.onGround;
         baseline = this.transform.position.y;
         moveDirection = new Vector3(0,0,0);
     }
 
     void Update()
     {
         switch (playerState)
         {
              case State.onGround:
                  DoOnGround();
                 if (Input.GetButtonDown("Jump"))
                  {
                      playerState = State.jumping;
                  }
                 break;
 
             case State.jumping:
                 Jumping();
                 moveDirection.y = jumpSpeed;
                 if(transform.position.y <= baseline)
                 {
                     speed = groundSpeed;
                     playerState = State.onGround;
                 }
                 break;
         }
         transform.Translate(moveDirection * Time.deltaTime);
     }
 
     void DoOnGround()
     {
         transform.position = new Vector3(-6.8f,0,0); // This just sets it at the start to be on the left side of the screen rather than 0,0,0 which is the middle
     }
 
     void Jumping()
     {
         moveDirection.y -= gravity * Time.deltaTime;
     }
 }

This is what my code looks like, it's a mess and I'm kinda brain-fried right now, but essentially what happens is I either just shoot off into space, or now that I've added * Time.deltaTime to transform.translate's movedirection, I just ascend slowly into space.

I've looked at a few other examples but honestly I'm not sure why it's just shooting off rapidly into space , the y going in the 1000's, or in the case of my code here with the added deltatime, slowly ascends into the abyss. Should it not come down with moveDirection.y -= gravity * Time.deltaTime; ? I'm a bit confused and I've like re-worked my code a fair bit, but removed my comments so it doesn't look disgusting to view.