This does NOT prove that the earth was smaller. The science books, while explaining plate tectonics, have always recognized that the continents fit together. This has been proven by fossil evidence among other geological evidence. It simply means that the large continents of ancient times broke apart.
How can it be claimed that there are too few subduction zones? If you can't prove they exist, you also can't prove that they don't exist.
How does this expanding earth theory account for mountain ranges that have been clearly been formed by lateral compression? This is something that can be seen 1st hand... you can walk up to the outcrops and see the evidence.
'Cause there's a monster on the loose