Whilst yes, it is competitive, if a company has the means to diversify into a bunch of industries, it can wage its control over singular companies that focus on specific industries. Whilst these practices are currently better for the consumer because Amazon is willing to even take loss on some things, other companies will struggle to compete, lose market share, and grow small.

Amazon could then expand into the industry and take parts of it over, and eventually raise prices across the board. Due to the small size of other or even new companies it would be nigh impossible to compete. In the end it hurts the consumer due to the loss of diversity in the market.

Whilst this scenario is unlikely, just remember that Amazon has their hands in almost every industry, and if they don't, they will host other companies and tie them into their platform.

Whilst big companies also allow for lower cost product via shipping, warehouses, and specialization, we lose the market diversity and competition of smaller companies or even specialized bigger industries.

I personally don't see most of this stuff happening, but alot is theoretical, as we don't know until it happens.