That's interesting I switched from a kindle to an iPad mini a few years ago and except for reading outside in the sun, I didn't notice any downsides concerning the display.
I started with a 212 DPI display (PocketBook 626), then moved to Kobo, which is 300 DPI, and the effect was much more dramatic.
If you're not using displays all day long, you might not be straining your eyes much, and may not be feeling it, too. Try using some artificial teardrops (without any additives, preservatives or active ingredients). If you feel relieved after using them, you're simply unaware of being uncomfortable, then.
I feel uncomfortable reading from a high quality OLED (iPhone X) or IPS panel (Apple MacBook Pro displays and an HP EliteDisplay) after reading for an hour or so, but when I open my Kobo Glo HD, I can read for hours without eye strain or feeling uncomfortable, even with front light. It just feels natural and doesn't make my eyes dry, forehead stiff or feeling exhausted. This is a study I'm conducting myself for 5+ years. So, it's enough of a data for me.