Thanks for your question.
What Rudolf Steiner taught us, is that humanity is in the current situation and evolutionary frame, because divine guidance allowed for some 'counterforces' to exist. Today we call this evil, but they can better be seen as spiritual beings that are out of phase, to early or to late, versus our development. That way they provide resistance, and a consequence is the strengthened development for humanity. The reason why divinity allowed this, is for a real big idea: freedom of choice. Up to now the spiritual hierarchies are interlinked and carry forward and execute impulses from above downwards, but there is no such thing as free choice. Humanity, as the tenth hierarchy, is the first hierarchy that is set free from creation. Freedom is required for true selfless love. Bottom line, there is an exciting new development here, which is why it is said the gods are really watching humanity and Man is the crown of creation. See the topic page Evil (and eg Schema FMC00.427) for an overview.
Now to your question: to cut a long story short .. the above decision rippled through the hierarchies and resulted in what is called the luciferic infection. Angels that didn't finish their development on Old Moon now take the opportunity during the Earth cycle, but they do that 'in Man'. See Schema FMC00.238 (tip: suggest you always right click to open links in new tab)
The impact of this is vast, and now we come to the answer to your question. The best place to start reading is: Luciferic influence on Man#A very different world, and a bit lower on the same page are links to the many different aspects that this brought about versus 'a plan without': Luciferic influence on Man#Consequences of Luciferic infection for Man. And one that will probably interest you to read (as someone already asked a related or similar question before), is this: Q00.002 - timing of the Mystery of Golgotha .. because under point 2.1.3 is described how Man's consciousness would have been very different.
Now this is not the end of the story, as we haven't covered the further consequences of the Ahrimanic and Soratic counterforces, but the above is the first most important aspect to understand. We can come back on the rest, but have to keep things a bit concise here to not get side-tracked.
Bottom line to your question: we, and the cosmos, gain much more ultimately this way, even though it comes at a price. But note: what is also important is how we interpret and live the meaning of suffering and sacrifice: in the spiritual scientific worldview they gain a different meaning.
Hope I read your question correctly, and that the above answers or at least puts you on track for further reading.
PS: This is a broad topic, and as you will see one has to study its various aspects. As you probably know or have found, the GA is a jigsaw puzzle with some 50.000 or 100.000 pieces (you could say pages, or 5000 lectures with 10 or 20 topic fragments or aspects). What this site tries to do is provide a top level interface layer to that to facilitate the study process.
Now if you would just read the GA lectures, you'd also get there, but it would take many years .. however that approach has the advantage you're doing it organically and 'overall', as a worldview shift, all contents and topics at the same time in parallel as you work through and process the huge amount of information. Which has other benefits as well as challenges, hence this site is intended bring insights through enhanced efficacy of the study process itself. The key however remains your own mind and soul work.