Пусть чечевица и варится дольше, суп из неё всё равно получается сытным.

Not exactly. In this sentence, пусть is not the imperative-style let meaning.

Here it introduces a concession, so it means something like:

• granted that
• even if
• although

So Пусть чечевица и варится дольше... means roughly Granted, lentils do take longer to cook... or Even though lentils cook longer...

Russian пусть can do both jobs:

• Пусть он войдёт = Let him come in
• Пусть это и сложно, мы попробуем = Even though this is difficult, we’ll try

Here и does not really mean and in the normal additive sense.

In the pattern пусть ... и ..., и helps create a concessive meaning: even though / granted that. It strengthens the idea that the speaker is admitting something, but then moving on to the main point.

So the structure is:

• Пусть X и Y, Z всё равно...
• Granted that X is Y, Z still...

In your sentence:

• Пусть чечевица и варится дольше = Even though lentils do take longer to cook
• суп из неё всё равно получается сытным = the soup still turns out filling

Yes. A very natural alternative is:

Хотя чечевица варится дольше, суп из неё всё равно получается сытным.

That would be a straightforward although sentence.

The difference is mostly stylistic:

• хотя = neutral, common, direct
• пусть ... и ... = slightly more rhetorical or emphatic, as if the speaker is conceding a point before giving the real conclusion

So пусть ... и ... can sound a bit like:

• Yes, that may be true, but...
• Granted..., still...

Because вариться and варить are different verbs in use.

• варить = to boil/cook something
  
  • Я варю чечевицу = I’m cooking lentils
• вариться = to boil/cook, referring to the food itself
  
  • Чечевица варится = The lentils are cooking / Lentils cook

So in this sentence, the subject is чечевица, and the meaning is lentils take longer to cook, not someone cooks lentils longer.

This is a very common Russian pattern with food:

• Картошка варится быстро = Potatoes cook quickly
• Фасоль варится долго = Beans take a long time to cook

Because чечевица in Russian is normally treated as a mass noun, not a plural count noun.

So Russian usually says:

• чечевица = lentils / lentil as a foodstuff

This is similar to how English says rice rather than rices.

So even though English usually uses plural lentils, Russian naturally uses singular чечевица when speaking about the ingredient in general.

That is also why later the pronoun is singular feminine:

• из неё = from it / from it (i.e. from lentils)

Дольше is the comparative form of долго.

• долго = for a long time
• дольше = for a longer time / longer

So варится дольше means takes longer to cook.

Russian often leaves the comparison unstated if it is obvious from context. So дольше does not need an explicit than... in order to sound complete.

If you wanted to be explicit, you could say something like:

• чечевица варится дольше, чем рис = lentils take longer to cook than rice

But here the sentence works fine without that.

Because из requires the genitive case, and after prepositions Russian personal pronouns often take the н- form.

For она, the relevant forms are:

• without a preposition: её
• after many prepositions: неё

So:

• её = her / it
• из неё = from her / from it

This happens after many prepositions:

• у неё
• от неё
• для неё
• из неё

Since чечевица is feminine singular, the pronoun is also feminine singular.

Here всё равно means:

• all the same
• nevertheless
• still
• anyway

It shows that the second clause remains true despite the first one.

So the logic is:

• Yes, lentils may cook longer
• but the soup is still filling

Without всё равно, the sentence would still be possible, but всё равно makes the contrast much clearer and more natural.

Compare:

• Хотя чечевица варится дольше, суп получается сытным.
• Хотя чечевица варится дольше, суп всё равно получается сытным.

The second version more strongly emphasizes despite that.

Because after получаться in the sense of to turn out / come out / end up being, Russian very often uses the instrumental case for the resulting quality.

So:

• сытный = nominative
• сытным = instrumental

This is a common pattern:

• Суп получился вкусным = The soup turned out tasty
• Фильм оказался интересным = The film turned out to be interesting
• Он стал врачом = He became a doctor

In your sentence:

• суп получается сытным = the soup turns out filling

That instrumental marks the quality the soup ends up having.

Сытный is used for food, not for a person.

It means:

• filling
• substantial
• hearty

So сытный суп is a soup that satisfies hunger well.

A related word is сытый, which describes a person or animal:

• Я сытый / Я сыта = I’m full
• сытный суп = a filling soup

So:

• сытный = about the food
• сытый = about the eater

Because the sentence has two clauses:

1. Пусть чечевица и варится дольше
2. суп из неё всё равно получается сытным

The first clause is a concessive clause, and the second is the main clause. Russian separates them with a comma.

So the overall pattern is:

• Пусть ... и ..., ... всё равно ...

This is a standard concessive structure, similar to:

• Хотя..., всё равно...
• Even though..., still...

The word order is fairly flexible, but the given version is natural and clear.

The sentence highlights the contrast nicely:

• first, the concession: Пусть чечевица и варится дольше
• then, the main point: суп из неё всё равно получается сытным

You could also hear variations such as:

• Хотя чечевица варится дольше, суп из неё всё равно получается сытным
• Суп из неё всё равно получается сытным, хотя чечевица варится дольше

But inside the original sentence, всё равно is especially natural before получается, where it emphasizes the result:

• суп из неё всё равно получается сытным

So the word order is not absolutely fixed, but the version you have is idiomatic and well balanced.