It isn't really leaner. For it to be secure and non-custodial, it requires running a LN state machine on the device (eg VLS). So, for a single node and user, they must run two LN state machines. This increases complexity dramatically.

And, while it might sound simpler on the surface, it does not actually solve the big challenges of mobile non-custodial LN wallets. Offline receive is not solved by this. Multi-app interfaces are not solved by this. Backups are not uniqued solved this. In fact backups are more complex because you have 4 copies of the LN state instead of 2! You have the VLS local copy, the VLS cloud copy, the CLN/Greenlight copy, and the CLN/Greenlight cloud copy.

The only real benefit to the Greenlight model is to bundle up all the various server-based services that are needed for a LN wallet into a single provider, improving dev UX. However, that can be done with the LDK ecosystem too, it just hasn't yet (eg LSP, Esplora, VSS/backups, RGS, probing for payment success). Also, a single provider from either ecosystem weakens security and self-custody nature, as LN state backups ideally are not provided by the LSP.

Also, because the LDK ecosystem supports pathfinding on mobile (made performant with RGS and probing/scoring files), an LDK-based wallet has dramatically better privacy than having every single user payment sitting on Blockstream's servers.