Here are the problems with shifting defensive stats from health to resists.

Health is a generic tank stat, and as such it is effective against all types of damage. The problem however is that anyone who builds health becomes tanky far too easily. Ideally, we would think, if we changed the value of big defensive items to be more focused on their resists, tanky champions wouldn't have such a large first item power spike.

That's great and all, but it comes with many issues. Firstly, in changing the gold per stat efficiency of any defensive item, you need to give it disproportionately more power in its respective defensive stat in order to have the item remain valuable. The reason for this is, since health provided a generic defensive stat, items with health and resists needed to be less effective at defending against any particular one. Having more resists and less health means it needs to be much better at reducing damage of that type to make up for the loss of health or not be nearly as valuable as before. Essentially, champions need to do significantly less damage to enemy champions who build items that have the appropriate resistance to make up for the extra damage that the other damage type can do.

Next, any and all sources of true damage and armour pen have been disproportionately buffed due to smaller health pools. Less health and more resistances means the value of penetration and true damage are much higher than they were initially balanced to be. This should result in inflated winrates of champions with these things innately in their kits. Additionally, although they nerfed penetration on items, the value of pen shoots up so significantly that these items still more than pull their weight in value where the items with stat swaps don't. Also, looking at void staff as they didn't change the % pen at all.

Furthermore, the excess amount of resistances and lack of health lead to unclear scenarios where the person who is the tank isn't as visibly tanky. Having more resistances and less health may work, but they also significantly reduces clarity of tankiness. People with 4000 hp we could tell were tanky because their health bar had more lines in it than those who weren't tanky, but 300 armour on 2000 hp looks like the same tankiness as 50 armour on 2000 hp. Not only does this leave one baffled as to why that 2000 hp malphite won't die, but also leads players of tanks to feel incredibly squishy despite their resistances.

Finally, and perhaps most importantly of all, every CHAMPION in the game was balanced around havinhigher health pools and lower resistances. Not only does this mean a significant number of tanks will likely be disproportionately weaker after the changes, it also makes others disproportionately strong. Any kit with % hp damage does less damage overall, and any champion who relied on a singular tank item for a large portion of their usefulness (every tank builds sunfire, which basically got mega nerfed) are put in a significantly worse spot than before. Any champion kit that relied on flat damage and pen to keep them relevant late game got buffed. And all tanks, who were balanced by getting punished in early lane, are now significantly weaker die to only being able to itemize against one type of damage effectively.Understandably this was going to happen, but as a tank player I feel incredibly unsatisfied playing the game in this state.

(TL;DR)So, there are four major issues with the new system. Resists needs to be significantly more valuable than before, true damage and pen need to be tuned down both in kits and on items, clarity and satisfaction of tankiness has been reduced, and every champion balanced around previous itemization is either much stronger or much weaker than they should be.

Some of these issues are easier to fix than others, like the balance of individual tanks, but others are simply a symptom of the changes made and CAN'T be fixed unless the update was reverted, like the clarity of tankiness. Personally, I'm going to continue attempting to play the game, but from my experience thus far I doubt I will be coming back to it much.

Leave any comments or concerns below, and tell me what you think of the changes.