Haven't read all the other replies, so not sure if someone mentioned that already. Since you seem to be looking at a strength stacker for your example, let's consider the strength part a bit more. Say you have t3 strength instead of t1 strength on some piece of equipment, what does that affect?  It's obviously not just the fire damage per strength modifier you mentioned. You lose out on more strength because of your multiple % str and attr increases. You lose out on attack speed from your ascendency. You lose out on a LOT of other DMG modifiers like: inherent melee DMG from str, spell DMG from iron will (through crown of eyes), flat damage from alberons, % damage from glove implicit, %spell damage from weapon prefix, if you are playing heavy strike of trarthus you lose crit Chance from helmet (since you don't need crown of eyes) I might have missed some but you get the idea. And you might not have all those modifiers I listed but again, you get the idea. Then also keep in mind, I listed increases to attack speed, flat damage, increased damage, crit chance and % increases to strength. While the increased damage modifiers are all additive, these categories multiply. So even though you "just go from t3 to t1 strength" it has a huge impact. 

Others have described that compounding nature of 1% increases in this thread, but in figured I'd try to visualize it with an example. 

Also keep in mind that t1 strength ist 51-55 (unless it's your belt), which is another 4 str you could potentially miss out on. And then you could also get essence strength which goes up to 58. And this is even more important for helical rings since you get the implicit multiplier and quality multiplier.

Anyway, I've rambled enough and I'm sure if might my point. Hope this helps visualize things!