Got your message right here before you shoot me anything haha..
I would like you to read the following linked:
https://www.audioholics.com/av-receiver-reviews/denon-avr-x3300w-1/measurements
https://www.soundandvision.com/content/denon-avr-x3400h-av-receiver-review-test-bench
The X3300W and X3400H's amp sections are very likely the same so the above linked bench test results should apply to both. The X3400H has a slightly better DAC chip and a few additional features.
Then you can use the linked calculator to find out how much power you need, and that should tell you if your sales rep just bs you or not.
https://myhometheater.homestead.com/splcalculator.html
if you have trouble using that calculator, just tell us you seating distance, room dimensions, and how loud you listen (e.g. as loud as that in a movie theater, or much quieter), or even the highest volume setting you ever use when watching your favorite action movie should give us some hints, assuming you did run auto setup/Audyssey.