Given the constraint (3.5 hours of model effort) having a Lean proof is actually a sign that some of the results are likely weak. Despite the community efforts, the mathlib has many gaps and lacks many basic theories. So many problems can not even be stated yet not to mention proved. And formalization steps are small and labor intensive, so you are often constrained in how far you can go by the volume of code you produce. It's also telling that Lean tooling isn't advanced by the labs despite the resources they put into their effort, the importance they attache to Lean and the frictions they must have run into constantly. The release feels more like a retreat by the labs.