It was intended to be like that from the beginning and it’s better because until you cand make a zodiac box that contains a talizman ( amongst other useless items) you will never gey the chance to up it not even to +5

The "right" elementary force increase the damage of about 20~30% no matter how much it is.
The same thing is valid for resistances, no matter if you have 1 / 10 / 50 wind force, if your opponent have a set amount of wind defence the damage is reduced by the same % amount.

The "elementary force" in general increases the damage against everything for a very little amount but since talismans can reach +200 the potential is huge, bar the fact that on live servers are almost impossibile to obtain and very hard to upgrade.

It's natural. The more bonuses you combine, the greater the effect. For example 1 avg, 1 devil and 1 monster does more than 3% of each apart. It's the same when you have 0 mob, 0 avg and lots of devil, and you put 1 mob the effect is increased alot. So yea the elementary force is just another effect