Read what you just wrote and are trying to compare. Gamebryo by itself is a decent RPG engine, but Bethesda's modified builds are garbage. Hastily put together in an effort to assemble Morrowind 20 years ago, the reason why Bethesda games are so buggy. They use a modified engine that skipped most of it's debugging stage to save on costs and ship on time, and when the time came to update and upgrade for Oblivion, they never rewrote the engine properly or addressed the bugs and spaghetti code, but rather just built on top of it; like building a house over a rickety bridge. And they did the same thing again for F3. Their half-assed Creation engine is still based on Morrowind code so the bugs stick regardless, as with F4 and F76. You think the people who coded Morrowind still work at Beth or that BGS has a blueprint and log of engine source code from 1999? Hell, BGS Austin really must've hated Todd after he had them try and program multiplayer on an engine made for SP and that breaks so easily when trying to add more open variables like extra players.