> Sorry, I meant inter-satellite. Iridium’s inter-satellite capability is highly limited and irrelevant for emergency comms.

It absolutely isn't, where are you getting this from? Both routine and emergency communications regularly traverse inter-satellite links. For a while, Iridium only had a very small number of operational ground terminals; nothing would work without inter-satellite links in that scenario.

> In ideal conditions. 5 watts vs something like 1.6 makes a huge practical difference.

Can you name a scenario where you'd get a signal through to a satellite with 5, but not 1.6 watts? This is absolutely negligible; even just rotating your transmitter ever so slightly will make a much, much bigger impact.

I have never not received an Iridium signal when there was line-of-sight to the satellite.

> There is a reason 406 MHz is the requirement for aviation.

Aviation and marine safety of life specifications care a lot about redundancy and availability. COSPAS-SARSAT is conceptually very simple and does not require ongoing subscriptions, so it makes for an excellent fallback option if other communication methods are unavailable.

For example, for passenger or cargo ships, you need at least two other bidirectional means of long-distance communication when crossing oceans. For polar routes outside of geostationary satellite coverage (i.e. Sea Area A4), the only real options (certifiable under SOLAS/GMDSS regulations) are HF radio and Iridium.