Hardened kernel (e.g Coppherhead OS), custom open-source ROM to disable all telemetry and audit the code (among others), FOSS APK provider (f-droid), disabling online tracking (AdAway, AFWall), full filesystem access. iPhone hardly has any of this.

Note that this is true of any bootloader-unlocked Android phone, not just security-focused ones.

Please bear with me, I'm not OS-savvy, are many of these features designed to protect against untrusted processes? If both phones have no additional apps installed, what would be the most likely way for the data within to be compromised? Is it fair of me to believe it's fair to distinguish telemetry and security as separate concerns?

Very telling that this is downvoted.

In general HN has a strong bias toward Apple over Android RE: security. Many of the points are entirely valid, but it's also true that some important advantages on the Android side (such as those listed above) as often understated or overlooked here.

For me, a closed-source OS is a dealbreaker on its own, regardless of any other major HW or SW advantages.