Deriving from Promise class can slow down things

Deferred.mjs

void async function() {

  // extending Promise
  class PromiseEx extends Promise {
  }

  // extending Promise as Deferred
  class Deferred extends Promise {
    resolve;
    reject;

    static get [Symbol.species]() { 
      return Promise; 
    }

    constructor() {
      let args;
      super((...a) => args = a);
      [this.resolve, this.reject] = args;
    }

    // this adds even more overhead:
    /*
    then = super.then.bind(this);
    catch = super.catch.bind(this);
    finally = super.finally.bind(this);
    */
  }

  // containing a Promise
  function createDeferred() {
    let resolve, reject;
    const promise = new Promise((...a) => [resolve, reject] = a);
    return {
      resolve, 
      reject,
      promise,
      then: promise.then.bind(promise)
    };
  }
  
  // this test is slow on Firefox
  const iterations = /firefox/i.test(globalThis.navigator?.userAgent) ? 200_000: 3_000_000;
  const cached = Promise.resolve(); 

  // testing new Promise directly
  console.time("new Promise");
  for (let n = 0; n < iterations; n++) {
    let resolve;
    const p = new Promise(r => resolve = r);
    cached.then(resolve);
    await p;
  }
  console.timeEnd("new Promise");

  // testing new PromiseEx
  console.time("new PromiseEx");
  for (let n = 0; n < iterations; n++) {
    let resolve;
    const p = new PromiseEx(r => resolve = r);
    cached.then(resolve);
    await p;
  }
  console.timeEnd("new PromiseEx");

  // testing new Deferred()
  console.time("new Deferred");
  for (let n = 0; n < iterations; n++) {
    const d = new Deferred();
    cached.then(d.resolve);
    await d;
  }
  console.timeEnd("new Deferred");

  // testing createDeferred as thenable
  console.time("createDeferred as thenable");
  for (let n = 0; n < iterations; n++) {
    const d = createDeferred();
    cached.then(d.resolve);
    await d;
  }
  console.timeEnd("createDeferred as thenable");

  // testing createDeferred.promise
  console.time("createDeferred.promise");
  for (let n = 0; n < iterations; n++) {
    const d = createDeferred();
    cached.then(d.resolve);
    await d.promise;
  }
  console.timeEnd("createDeferred.promise");

}().catch(console.error);