Is assistive touch required because I'm not sure how durable the iPhone 6s home buttons are because I'm constantly pressing it.

I would not say it is required. I've never had a home button fail on me. My almost 1 year odl iPhone 6 continues to work just fine.

I doubt Apple would build a button that is designed to be pressed constantly and not make it resistant to such uses.

Yes there have been cases of home buttons failing, but its rather sporadic.

Unless you are out of warranty, I would not worry too much.

No, assistive touch is not required. The Home button is designed to be used. In fact, Home buttons going bad is a rather uncommon failure (unless the phone is damaged by impact or liquid).