Your salesman is mis-informed.
The ES330 has a five speed tranny. 4 (or D4 as you say) allows the tranny to shift up through first gear to fourth gear and does not allow the tranny to go into overdrive. D (no 4) allows shifting into overdrive.
Your pre-2002 ES300 had a four speed tranny.....D was the overdrive position, so your shift lever had P, R, N, D, 3, 2, 1
In either shift position the car will shift up through first, second, third and fourth the same from a standing start. The salesman is just skirting the subject.
The manual actually states using 4 instead of D when going uphills and when there is a prolonged load on the car.
You will not hurt the car, you will only hurt your gas mileage by using 4 instead of D. I just put it in D and let it go at that.
you can avoid most severe hesitations by not putting the pedal to the metal. Rapid acceleration can be achieved at 3/4 throttle with minimal hesitation. It takes time and trial and error to get aquainted with this method. My first insticnt was to stomp it, even from a red light.
steviej