I totally agree on the “occasional beast” part while I also totally disagree on the “old system less secure”. I’m pretty sure my AAD P2 protected, MFA secured, and Windows Hello for Business enrolled Surface Book is much more secure then a 6 digit pin a person can easily forward to anyone. In “light and quick” sharing scenarios it is more secure if the receiving end of the invite is less technical savvy and not enrolled in any AAD based workload. But as we (Microsoft and partners) are working for the same world domination in the cloud directory landscape as we did in the past for on-prem AD, the new solution is by far a less secure version. If the target audience is Gmail users (as in most demos) I totally agree the new solution is “more” secure compared to a poor google user signing of for a Microsoft Account (MSA) using his Gmail email address. Total confusion.
I’m coming from a shop supporting enterprise customers and while we also live and breath in AAD most B2B scenarios involves third parties already owning AAD identities. These scenarios are not the show cases that require the Microsoft “B2B Collaboration” process. It is light file and folder sharing and most of the times not Guest group membership what would be easy to setup for a typical end user hitting share in SharePoint. The Microsoft “B2B Collaboration” features (besides adding someone to an Office 365 group) are not self service ready compared what we had (some still have until end of the year) in SharePoint Online since the beginning of the service a few year ago.