These are slighly off due to the exact aspect ratio on the phone, but basically even the largest iPhone is still sports 40%-ish less display area than the iPad Mini
It's a huge difference if you try them both in hand
Additionally, going from iPad Mini to the smallest iPad Pro is yet another massive leap
I'd pondered it and spent a lot of time demoing both ... they are just used totally differently due to how much larger the 11" iPP is vs the Mini
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I have both the 14 Pro Max and the Mini 6 and would not classify them in the same size class; the difference is significant.