No it is not. Unless you can't buy basically the same stuff from lots of other places this is simple the usual whining about 'big cooperations'.

The reality is that amazon overs good prices and people like to shop there.

And yes, suppliers are gone complain, that amazon is evil, just like suppliers complain that walmarket is evil, just as suppliers always claim whatever larger reseller they sell to is a evil monopoly.

The definition of a monopoly in economics is if that seller can essentially employ monopoly pricing, but amazon prices are not incredible higher compared to the competition.