That may depend on the instance you're on and the communities others from your instance susbscribed to as well those you subscribed to.

Also, sorting matters a lot. If you go by popular post, i.e. hot or top, it's not surprising to see many rather left-leaning posts as it's the result of a majority of like-minded people. In that case you're absolutely right and make a good point. If you then change to scaled for example you may encounter more diverse posts. I saw a bunch of pro-NRA posts just yesterday by changing the sorting.

But that are the posts. In the comments that picture may become different. It's not as rare to me to encounter opposing views and sometimes clearly stuff which I wouldn't categorise as politically left.