Nice insightful deep look into IOTA tech, which I have been considering supporting recently, after Sirin Labs announced they would use IOTA on their New Mobile Phone product when launched highlighting security as its main feature . I will wait for IOTA to address the concerns you have raised in your investigation.
Quote from Sirin Labs https://www.sirinlabs.com website, Crowdsale due to launch soon:
“FINNEY™ devices form an independent blockchain network, a distributed ledger both scalable and lightweight, powered by IOTA’s Tangle technology and SIRIN LABS’ security ecosystem. FINNEY™ is free from centralized backbones and mining centers, capable of providing fast, fee-less and secure transactions.”