Something notable about Sword of Ruin and Beads of Ruin is that they are the first non-stat-stage scale factors in the history of the modern stat system that apply any amount of decrease to a defense stat.
The absence of such factors before was, it seemed, deliberate: the raw stat formula refuses to output a stat value of less than 4, even for a level 0 or 1 Pokemon with a negative nature in the stat and a low base stat. Combined with the +6/-6 cap, this means they can be divided by 4 but no further, so a 4-point stat (indeed, even a 7-point stat) will remain at 1 after all those drops. Other factors that claimed to make a Pokemon weaker to certain things, like Dry Skin or Fluffy, were always coded as an increase to incoming move power or damage, rather than admitting the existence of any factor that could ever possibly reduce a defense stat beyond what the stages already do.
Early on in RBY, you had some mechanics that understandably weren't very polished: if you Screeched the opponent's defense down to 1, you could then use Explosion to cut that value in half for the duration of the move. Or any physical move used with at least 256 attack into 3 defense would divide both values by 4, and get a 0 that way. This resulted in a division by 0, and a game crash. Modern games aren't quite as fragile when you throw those challenges at them, and will catch the attempted division by 0 before it happens, with the failsafe being to zero out the result of the calculation up to that point, and any attacks aimed at that side will do only single-digit damage no matter how powerful they are or if they're super effective. In effect, this means if you can get a 0-point defensive stat, the game will treat that as an infinitely high stat. The trouble, of course, lies in getting that zero in the first place--it requires either direct stat hacking, or Sw/Sh introduced a vector involving overflow of the positive nature calculation to the unobtainable Eternatus-E form (thereby introducing the mechanic to Pure Hackmons). It's clear from the damage-mitigation behavior of 0 defense that this failsafe mechanic was never supposed to be accessible for general use.
Did the Ruins change all that? If you stat-drop a low-level Pokemon down to 1 defense or SpD, then bring in the appropriate Ruin ability to affect that stat, will this result in a further reduction to 0, and if so then does the game still treat attempted division by a 0-point defense stat the same way it has based on the precedent of gens 5-8?