Seraphis was previously named ZCT and was a framework developed independently by Koe that did not have exact implementation details that would fit into it such as choice of proofs or addressing structures.
We shared our work on Lelantus Spark with Koe and our innovations with Spark addresses solved an open problem with ZCT's addressing system which then lead to Seraphis. This is why the addressing structures are quite similar. While similar to Spark, Seraphis is a framework rather than a protocol with full implementation details and does not yet have an academic style paper with full security proofs unlike Lelantus Spark.
Seraphis makes design choices for Monero by using it to scale ring sizes. Lelantus Spark on the other hand doesn't use decoy sampling and instead relies on large pools of anonymity combined with sliding windows between the pools. This offers much greater anonymity per transaction and avoids many of the problems with decoy selection algorithms at the cost of performance which can be mitigated with batching techniques.