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The key being endoparasitically. This sort of like comparing a home invasion robbery to a dinner party.

Parasitism is just a form of symbiosis. Parasitism grades into commensalism which grades into mutualism, and often is the initial step in the evolution of mutualism.

(On the other hand, so do home invasions and dinner parties. What about a guest who steals your silverware?)

Again, here you deal with the pre-existence of a complex cell establishing endosymbiotic relationships and this gets us no closer to the origin of membrane bound organelles than the symbiotic relationship between a crocodile and Trochilos.

Small prokaryote invades large prokaryote parasitically.
Parasite evolves not to kill its host, improving its own survival.
Parasitism eventually evovles into mutualism, so that both benefit from the symbiosis
Mutualism becomes obligate; eventually one organism loses much of its independent biochemistry.

Please identify the step you claim is impossible.

All these steps are seen, sometimes separately, sometimes all together, in symbiotic relationships.You have posted no good reason why they could not have occured in the evolution of eukaryotes. In fact, the only missing element is that AFAIK we haven't yet identified a clearly mutualistic relationship between a prokaryotic endosymbiont and a prokaryotic host. And of course we also have the genomic evidence that mitochondria and chloroplasts evolved from distinct free living organsims, such as the fact that they have prokaryotic ribosomes.

To refresh your memory, that has to do with the evolution of eukaryotes from a single celled organism without membrane bound organelles through endocytosis that leads to symbiosis.

And I gave you a series of examples in the first link I posted. Denial ain't just a river in Egypt. Bacteria are known to engage in endosymbiotic relationships with other bacteria. All the handwaving in the world won't wave that away.