Another difference is that JSONB is immutable. Suppose you need to replace one specific value inside an object or array. With JSONB, you would rewrite the entire JSONB document as a result of this, even if it is several megabytes large. If you are performing frequent updates inside JSONB documents, this will cause severe write amplification. Despite the fact that offsets are grouped in chunks of 32, Postgres still rewrites the entire document. This is the case for all current Postgres versions.
On the other hand, Lite³ supports replacing of individual values where ONLY the changed value needs updating. For this to work, you need separate offsets. Postgres makes a tradeoff where they get some benefits in size, but as a result become completely read-only. This is the case in general for most types of compression.
Also JSONB is not suited to storing binary data. The user must use a separate bytea column. Lite³ directly implements a native bytes type.
JSONB was designed to sacrifice mutability in favor of read performance, but despite this, I still expect Lite³ to exceed it at read performance. Of course it is hard to back this up without benchmarks, but there are several reasons:
1) JSONB performs runtime string comparison loops to find keys. Lite³ uses fixed-size hash digests comparisons, where the hashes are computed at compile time.
2) JSONB must do 'walking back' because of the 32-grouped offset scheme.
3) Lite³ has none of the database overhead.
Again, the two formats serve a different purpose, but comparing just the raw byte layouts.
