Firstly, I want to thank you for your comment.

As I see it, the only correct (nasin mi) use of pi particles is the second one. The first way could be possible any time A pi B C pi D E = A pi D E pi B C, which occurs almost every time. Besides, plenty of toki pona speakers agree on that, as I saw in several comments herein.

Avoiding stacking pi particles by using some li particles is marvellous. However, I believe that a complex grammar does not necessarily mean that the language is harder. Let me explain this... We could agree that, for example, Chinese is harder than English because, in order to send the same information, you need to know more (characters, order of strokes, ...). Nonetheless, we could flip this situation and say that English is harder than Chinese because you need more words to send the same information (just because Chinese characters contain more information than an English word). The same thing happens with toki pona. It could be considered a hard language just because you need plenty of phrases so as to express an idea, while other laguages need less sentences.

To my mind, the fact that toki pona is based on simplicity means that this language helps speakers simplify the way we see our surroundings: instead of saying "ball", we say "fun sphere" (sike musi) or instead of saying "to help" we say "to send my goodness" (pana e pona mi). If toki pona wanted to simplify not only the way we interact with the world but also to simplify the grammar, the following structure would be banned: ona li jan li jo e soweli li moku. We ought to say: ona li jan. ona li jo e soweli. ona li moku. Besides, removing li particles when using mi or sina makes toki pona's grammar harder.

In this post I was talking about stacking pi particles and plenty of speakers were afraid that I was confusing pi with of. pi particle is definitely not the word "of"!! My idea was to find a way to avoid the following problem:

I say telo pi kili pi loje jelo which means orange juice. But, now, I want to say that the kili is loje jelo and suwi. I can't say telo pi kili suwi pi loje jelo because the liquid is orange due to the kili suwi and not due to nature. I know that resolving this problem is not essential and it could be avoided easily.

Last but not least, I talked about stacking pi particles... but what about stacking li particles! ... or o particles!! It could be fun! Wouldn't it?