Firefox is slower, requires more RAM and uses more power on macOS now; it’s highly unlikely that essentially the same engine running on iOS would run significantly differently.
Of the mainstream browsers on macOS, Firefox has always been the slowest.
The goal is to preserve privacy by default--no extensions required. The vast number of users don't install them or wouldn't know which ones to install.
Brave is secure out of the box and doesn't require extensions to protect your privacy: https://brave.com/features/
Safari also doesn't require extensions to protect your privacy: WebKit Tracking Prevention Policy—https://webkit.org/tracking-prevention-policy/
Apple first shipped Intelligent Tracking Prevention in June 2017, long before Firefox or any other browser had anything similar: https://webkit.org/blog/7675/intelligent-tracking-prevention...
Safari’s Intelligent Tracking Prevention stops the cross-site tracking, fingerprinting, etc. by ad companies.
The ability to block content is built-in to macOS and iOS for 3rd parties to use.
As for Safari using less power and ram on mobile there is no evidence that Firefox would uae more of either since Apple doesn't allow it to run. As far as we know if other browsers were allowed to run some might compete on power and ram.
As for security, chrome on desktop has a superior track record. The CVE list proves this, so by denying competition Apple denies users more secure browsers.