FYI: I'm trying out an experiment where your Strength modifier also acts as a defense modifier (similar to the modifiers granted by Protect/Expose), as an attempt to close up some of the disparity between what Strength gets you (access to three largely similar elements: Slash, Impact, and Pierce, which share many of the same strengths and weaknesses) and what Magic gets you (access to pretty much everything else, including healing and strong ranged/area attacks) If it goes reasonably well on my end, I will include it in the upcoming build and we'll see how terrible it is.
Keep in mind the general modifiers associated with investment per level in a stat:
0 per level: -25%
1 per level; 0%
2 per level: +25%
3 per level: +50%
4 per level: +75%
5 per level: +100%
Thus, characters who put only 1/level into Strength will seem no different from before. Characters who skimp on strength will be somewhat squishier, characters who invest significantly in it will see potentially significant results.
Finally, due to how defense works in Demon, the proper way to view those percentages is not an adjustment to the damage taken, but rather, an adjustment to how long your HP last. ie: If you have 50 HP at 0 per level Strength, it will feel like 37.5 HP. If you have 50 HP at 2 per level Strength, it will feel like 62.5 HP. Critically, +100% defense, while very nice (meaning your HP last twice as long as they normally would), does not mean you're just immune to everything.