there are only minor elements that armada2 and legacy have in common, and definitely its not the core game engine

Armada2 uses a software render for many elements, for example

nobody would use a 10 year old engine.. they just recycled some parts, like ODFs, but thats just the input format, not the engine itself. They are not the same engine and not linked to armada2 exept some makeup on the outside.
To quote the development team:
Star Trek®: Legacy and Tactical Assault, are they "complete builds" (new game engine) or are they based on existing gaming engines, if so, what engines are they based on?
At Mad Doc®, we’re capitalizing on our years and years of experience with Star Trek games, and we’ve actually been working on the core graphics engine for Legacy as its own new engine since 2002. Now we have platforms powerful enough to give us a result that looks downright cinematic – it’s why we’re doing the big push on Legacy and the game engine now. And let me just say, it’s paying off, because the game is looking spectacular!
Yep, there are plans for hull damage, but thats not possible at the moment. we would like to do something about that in future engine upgrades, but that still requires a lot of development

we are working on it, though
And yep, the green blob is a torpedo