As far as I'm aware T3 arti haven't been changed since I've been playing (coming up to 2 years now I think), but I can't speak to before that. In terms of M27 always building T3 arti, it'll largely be down to what its opponents do - it's meant to get T3 arti if dealing with someone who is turtling heavily and/or in the late game, but you can vary the setup to vary the chances. For example, just play against 1 M27AI (if you're against multiple then one of them is more likely to try and eco and rush a t3 arti), or a map where navy plays a bigger role. On maps with a chokepoint (assuming 1 M27AI per chokepoint such as 2v2 on Fields of Isis) it's also likely to invest resources into turtling which in turn can delay when it gets the arti.
In terms of T3 arti being strong though, it's only on certain maps where I'd see it as strong (dual gap, astro and similar). Almost every 4v4 TMM I've played (I'm around 1k rank so have had games with players from negative rank to 2k rank in them from time to time) it's ended before getting to the stage of game where T3 arti would have been effective because of how big an investment it is - i.e. it's generally far better to invest that same mass into navy (on a naval map) or on a land experimental, even though team games by their nature favour ecoing more (since most teammates will help defend an attack but won't support an attack, meaning if you try and be aggressive you often end up fighting more than one player at once).