What is the difference between でありながらも and でありながら?

Question

On this site, I came across this JLPT N2 question:

これはシンプルで　_______　純粋で魅力的なスピーチです

1. あってながら
2. あるながら
3. ありながら
4. ありながらも

I chose 4 while 3 is correct.

I was having difficulties choosing between 3 and 4. 1 and 2 are blatantly wrong. I eventually went with 4 because I always thought that も adds some "strength" or "emphasis", as in よりも sounds stronger than より

地球よりも大きい Even bigger than the Earth

So I thought ながらも works similarly in that it expresses a stronger 逆接 sentence.

This is an even though simple, but pure and charming speech.

I know the English sounds weird but the point is, I thought that も adds that word "even" there. I thought this would be appropriate here because the two things here are very contradictory.

I looked the ながら grammar up and all I could find were sites like this, which don't point out what different the も makes. The linked site seems to put も in parentheses as if to say that it's optional.

いったいなぜ３が正解なんですか？

Answer 1

これはシンプルで　_______　純粋{じゅんすい}で魅力的{みりょくてき}なスピーチです

1) あってながら

2) あるながら

3) ありながら

4) ありながらも

I know nothing about JLPT, but assuming that one is required to select the "best" answer instead of all of the "correct or feasible" answers, then I would feel that 3) would be the best or at least the most feasible answer.

First of all, 1) and 2) are not even grammatical, so they should be put aside from the start.

The choice between 3) without the emphatic 「も」 and 4) with should be made by assessing the amount of contrast between 「シンプル」 and 「純粋で魅力的」. Would most people consider these two sets of qualities truly antithetical to each other? If so, 4) with 「も」 would be the best (or most feasible) answer.

I, for one, do not think there exists "enough" antitheticality between those two sets of qualities to use the emphatic 「ありながらも」 to connect them. I would feel differently, though, if the two had been 「シンプル」 and something like 「奥{おく}が深{ふか}い」 ("profound").

Admittedly, where to draw the line bewteen the ありながら and ありながらも territories might indeed depend too heavily upon each individual's subjective judgement. If I could legally sue particles in the future, I would sue 「も」 first and foremost.

In the meantime, I just do not see enough unpredictability between 「シンプル」 and 「純粋で魅力的」 to use a 「も」. To me, 「純粋」 is so closely related to 「シンプル」. The two sets of qualities this time simply do not surprise me enough to make the use of 「も」 very valid.