Saying that the base game is a mess is quite unfair imho. I almost spent 800 hours in the game and never found a game breaking bug that made me say "ok this is unplayable". Yes there are some bugs and yes I am not into complex builds so i encounter less bugs compared to those who push the game at its limits and are way more skilled but I still enjoyed and achieved every content the game offered me, so I wouldn't consider the game broken at all and the DLC is more than welcome.
As for the DLC, the sole fact that it revamp the space rocket is a good addition to the end game content, hopefully it will make more sense than the current system. Another good thing is to be able to colonize more planets in 1 playtrough, something i even posted on a wish list thread some weeks ago.
I agree that some ingame mechanics are controversial and is hard to call them legit or exploits, but some others aren't and they are easy to detect.
Melting abyssalite with the refinery is not an exploit. It was probably unexpected from the DEVs but certnaly is not an exploit. Maybe with nuclear power we would reach those high temperature and melting abyssalite would be easier and less sofisticated.
Using a timer on a liquid tepidizer to heat the liquids above 80 degrees, is an exploit.