Instagram was and still is in a highly competitive market. Previously it was Snapchat at the time and now it's Tiktok. Not to mention YouTube shorts, Reddit, Twitter, and every other service focused on video and pictures.

I don't think any social media consumer is lacking choice.

Regardless of how much “choice” there is in a market, FB made an anti-competitive play. Now we all have n-1 choices.

The question of whether society should allow companies to perform anti-competitive actions should not be “will we be left with enough choices?”, but should be “is this an anti-competitive action?”