the blitz GC works just fine... it's not any more prone to *programmer created* leaks than what you just described.
Yes it is. The BlitzMAX GC simply counts references. The .Net and Java GC walk the stack. The BlitzMAX way of doing it is marginally faster (when you're in a single threaded environment) but prone to memory leaks with objects that use cyclic references. All entities have a link to the world for fast iteration.
Walking an array is not faster than walking a tree.