I can get GameScene:SKScene to appear using the layout constraints, but why can I still draw inside the safe ares?

Code Block 
import UIKit
import SpriteKit
import GameplayKit
var myGlobalVars = GlobalVars(backGround: SKSpriteNode(),
                              pegHolder: SKSpriteNode(), currentNode: SKSpriteNode(),
                              widthPoints: 0.0, heightPoints: 0.0,
                              widthPixels: 0.0, heightPixels: 0.0, passGo: false, sceneRect: .zero, fileName: " ")
class GameViewController: UIViewController {
    private let myView : UIView = {
        let myView = UIView()
        myView.translatesAutoresizingMaskIntoConstraints = false
        myView.backgroundColor = .clear
        return myView
    }()
    
    private func addConstraints(){
        var constraints = [NSLayoutConstraint]()
        
        constraints.append(myView.leadingAnchor.constraint(equalTo: view.safeAreaLayoutGuide.leadingAnchor))
        constraints.append(myView.trailingAnchor.constraint(equalTo: view.safeAreaLayoutGuide.trailingAnchor))
        constraints.append(myView.bottomAnchor.constraint(equalTo: view.safeAreaLayoutGuide.bottomAnchor))
        constraints.append(myView.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor))
        
        NSLayoutConstraint.activate(constraints)
    }
    
    override func viewDidLayoutSubviews() {
        super.viewDidLayoutSubviews()
        let topSafeArea: CGFloat
        let bottomSafeArea: CGFloat
        if #available(iOS 11.0, *) {
            topSafeArea = view.safeAreaInsets.top
            bottomSafeArea = view.safeAreaInsets.bottom
        } else {
            topSafeArea = topLayoutGuide.length
            bottomSafeArea = bottomLayoutGuide.length
        }
    }
    let logo = UIImage(named: "startup")
    override func viewDidLoad() {
        super.viewDidLoad()
        view.addSubview(myView)
        addConstraints()
        
        if let view = self.view as! SKView?
        {
            
            myGlobalVars.widthPixels = UIScreen.main.nativeBounds.width
            myGlobalVars.heightPixels = UIScreen.main.nativeBounds.height
            myGlobalVars.widthPoints = UIScreen.main.bounds.width
            myGlobalVars.heightPoints = UIScreen.main.bounds.height
            var scene : GameScene!
            DispatchQueue.main.async { [self] in
                     scene = GameScene(size: CGSize(width: myView.frame.width,
                                                       height: myView.frame.height))
            scene.anchorPoint = CGPoint(x: 0.0, y: 0.0)
                scene.backgroundColor = .clear
                scene.scaleMode = .aspectFit
                myGlobalVars.sceneRect = scene.frame
                myGlobalVars.gameScene = scene
                view.isHidden = false
                view.presentScene(scene)
            }
            myGlobalVars.passGo = true
            
            view.ignoresSiblingOrder = true
            view.showsFPS = true
            view.showsNodeCount = true
        }
    }
    
    override var shouldAutorotate: Bool {
        return false
    }
    override var supportedInterfaceOrientations: UIInterfaceOrientationMask {
        if UIDevice.current.userInterfaceIdiom == .phone {
            return .allButUpsideDown
        } else {
            return .all
        }
    }
    override var prefersStatusBarHidden: Bool {
        return false
    }
}

While it works, am not sure why

Am I getting lucky? Or is this bound to crash?

Code Block 
import UIKit
import SpriteKit
import GameplayKit
class GameViewController: UIViewController {
    @IBOutlet weak var myView: SKView! //<-
    override func viewDidLoad() {
        super.viewDidLoad()
        
        if let view = self.myView { //<-
            // Load the SKScene from 'GameScene.sks'
            if let scene = SKScene(fileNamed: "GameScene") {
                // Set the scale mode to scale to fit the window
                scene.scaleMode = .aspectFill
                
                // Present the scene
                view.presentScene(scene)
            }
            
            view.ignoresSiblingOrder = true
            
            view.showsFPS = true
            view.showsNodeCount = true
        }
    }
    override var shouldAutorotate: Bool {
        return true
    }
    override var supportedInterfaceOrientations: UIInterfaceOrientationMask {
        if UIDevice.current.userInterfaceIdiom == .phone {
            return .allButUpsideDown
        } else {
            return .all
        }
    }
    override var prefersStatusBarHidden: Bool {
        return true
    }
}

Not using storyboard at all.

Your myView is still a UIView, not SKView. Your view is still an SKView, not UIView.