How do text sizes compare between iPhone X, 8/Plus and SE?
Identical between pre-X devices; +17% with Zoomed-View; +7% on X

On SE, 8 and 8 Plus (and older devices of same form factor) text size is the same between devices, larger screen fits proportionally more text.

Zoomed View gives exactly the smaller-device amount of text in proportionally larger text size. 8 Plus screen is 17% larger than 8's, and SE is 17% larger than 8 (measured by screen height / width).

Conversely, on X the text is size in the middle of Standard-View and Zoomed-View of earlier devices, roughly:


7% larger than on 8 (proportional to how X screen is wider than 8)
9.5% smaller than on 8 Plus in Zoomed-View (proportional to how 8 Plus screen is wider than X)


DPI has no effect to text size on the apps I tried, no matter whether or not they support DynamicType system setting.



Notes:


%% diffs are between width of equal text in equal apps, with identical settings
screen width diffs are based on official specs: screen size in pixels divided by PPI
measured and researched on my own; I would appreciate link to an authoritative source or suggestions on better metrics