In other words, Esperanto is the worse-is-better universal language. Unfortunately for both Esperanto and Lojban, English is worse-is-better than both.
WRT English, there's nothing inherent to it that makes it the lingua franca of the world, it's just that it's the language of the dominating socio-economic powers since the British Empire. How quickly Mandarin is becoming popular around the world is a modern evidence to how economics play a role in determining the cultural appreciation of a particular country.
And "the knowledge of Esperanto can be transferred to other prominent languages"? Only in the most cursory ways! Esperanto's vocabulary is also deeply minimal: for example, it makes antonyms from the prefix mal-, so that 'big' is granda and 'small' is malgranda, and it makes heavy use of affixes and word-combining to generate new chunks of vocabulary: a school is a learn-place (lernejo), lunch is day-eating (tagmanĝo), a dictionary is a word-group (vortaro), and so forth. This is great for making a minimal vocabulary that can be easily learned, but it means that you get only a tiny fragment of knowledge that's transferrable to other languages.
I could go on about how the structure is actually deeply unnatural and reflects several odd choices, or how the pronunciation involves tricky to near-impossible consonant clusters (e.g. because s is pronounced as 'ts', the word eksciis 'realize' has the cluster kssts!), but it's really not a well put-together language in the way that this seems to imply it is.
I have heard other Esperantists describe the document as maybe harsher than it needs to be, grouping in the mountains with the mole-hills, but I think most of the things it describes are pretty uncontroversially considered to be flaws with respect to the language's original intent. Most of the speakers I interact with would say, "Yes, but what's your point?" But on the other hand, neither I nor the Esperantists I interact with regularly tend to be the types that think Esperanto still has a viable chance of becoming a true international language: we simply think it's a fun language to learn and speak. So it's possible that more radical Esperantists would disagree with our position there!
For the rest, I really appreciate the "insider" view you give. A couple points, though:
- It's not said that a language that borrows a word will keep its original pronunciation too. The very word pronunciation, for example, the various pronunciations thereof in English, French, Italian, Spanish would not be easily recognisable as a cognate to the untrained ear. "Transformation rules" need to be learnt to make use of vocabulary similarities across languages.
- The "near-impossible consonant clusters" do occur in many natural languages. Armenian and Georgian, for one, are known for some wild consonant clusters they have. Furthermore, that "ksts" one exists in English: texts, sexts; and not radically more difficult than say the greek φθάνω.