To get linear time validation, you need conditions at each control flow transfer that can be checked locally but together imply that stack usage in the function is well-formed.

The funclet approach (in more ordinary terminology) is to ensure that the stack difference from function invocation upon entry to a basic block is the same across entries to that basic block, and that those additional stack entries all have the same (statically specified) type in each invocation. This is very natural when generating code from an SSA optimizer.

Java bytecode traditionally didn't contain any of this branch target or type information, and required the bytecode verifier to do an iterative combined control/data-flow analysis. Even now that they added some of that type information with stack maps, it's still more complicated than it needs to be due to the historical legacy of this approach.