One of the features the phones had was that they could be remotely deleted and were locked down to prevent other apps on them. So an off the shelf iphone with signal is going to be vulnerable to having the device itself hacked via text message, bluetooth, or something else in a way the Sky ECC phones theoretically can't be, so it's not necessarily a slam dunk.

- Buy a cheap android phone from a no-name Chinese OEM.

- Run a basic script to disable app installs, phone calls and some other features.

- Never update the OS. Don't do any security patching.

- Write your own encrypted messaging app with your own crypto. Don't get any external reviews or audits.

- Resell this as a Sky ECC phone with some marketing dollars labeling it as "secure" and "private".

What do you think is more hackable, this or a regular iPhone/Samsung Galaxy/Pixel?

These are common requirements for a corporate phone.

Remote wipe is provided by both Android and iPhone iirc even to end users.

A stock android phone, a knowledgeable user could already remove a bunch of stock apps.