The Traffic of Session and SimpleX runs across 1000´s of relay.

Do you really think thats more secure?

They do NOT know hows behind all those relays.

Can be hosted by AWS or Google and can easily collect all the metadata of their users. For example IP-Adresses.

ONLY Threema does not collect any metadata or IP-Adresses.
Look for your self: https://threema.ch/en/transparencyreport

The centralization of Threema is a security feature.

Session & SimpleX are (meta)data-spreader !