De no ser por la estimación, empeoraría el rendimiento.

It means if it were not for or were it not for.

So:

• De no ser por la estimación... = If it weren’t for the estimate / estimation...

This is a fairly formal, compact way to introduce a hypothetical condition.

Both are possible, and they mean almost the same thing.

• De no ser por la estimación, empeoraría el rendimiento.
• Si no fuera por la estimación, el rendimiento empeoraría.

The version with de + infinitive is more compressed and often sounds more formal or written.
The version with si no fuera por is usually more transparent for learners and very common in everyday Spanish.

So de no ser por is basically an alternative conditional structure.

Because this pattern is built as:

• de + infinitive

So here:

• de no ser por...

This is a fixed grammatical structure in Spanish. It often expresses something like if not for..., unless..., or were it not for...

Compare:

• De tener tiempo, iría. = If I had time, I would go.
• De no ser por ti, no lo habría logrado. = If it hadn’t been for you, I wouldn’t have achieved it.

So the infinitive is not random; it belongs to this specific structure.

Because the sentence expresses a hypothetical result.

The logic is:

• If it weren’t for the estimation, performance would get worse.

That kind of unreal or imagined consequence is commonly expressed with the conditional in Spanish:

• empeoraría = would worsen / would get worse

Even though there is no explicit si, the condition is still there, implied by de no ser por.

It is usually understood as a hypothetical present or a general hypothetical situation.

• De no ser por la estimación, empeoraría el rendimiento. = If it weren’t for the estimation, performance would worsen.

This does not normally describe a simple future fact. It describes what would happen under a different set of circumstances.

The exact time reference depends on context, but the most natural reading is present counterfactual or general hypothetical.

The subject is el rendimiento.

So the structure is:

• empeoraría = would worsen
• el rendimiento = performance

Spanish often places the subject after the verb, especially in more formal styles or when the sentence begins with a long introductory phrase.

A more straightforward order would be:

• De no ser por la estimación, el rendimiento empeoraría.

Both are correct.

Because Spanish word order is more flexible than English word order.

In this sentence, putting el rendimiento after empeoraría is perfectly natural, especially because the sentence starts with the long conditional phrase De no ser por la estimación.

Spanish often does this:

• to sound more natural,
• to put focus on the verb,
• or simply because the context already makes the subject clear.

So:

• el rendimiento empeoraría
• empeoraría el rendimiento

Both are grammatical, though the first may feel more neutral to a learner.

It can mean both, depending on how it is used.

1. Intransitive: to get worse / to worsen

   • El rendimiento empeoró.
   • Performance got worse.

2. Transitive: to make worse

   • La falta de sueño empeoró la situación.
   • Lack of sleep made the situation worse.

In your sentence, empeoraría is intransitive:

• el rendimiento is the thing that would worsen.

So here it means would get worse / would worsen.

In this expression, por introduces the factor responsible for something.

• ser por X in this kind of structure points to the cause, reason, or factor something depends on.

So:

• de no ser por la estimación literally suggests something like
  if it were not because of / if it were not for the estimation

You do not need to analyse it word by word every time; it is best learned as the fixed expression de no ser por = if it weren’t for.

Yes, but it sounds fairly formal or technical.

Estimación can mean:

• estimate
• estimation
• sometimes assessment, depending on context

In technical, academic, economic, or statistical contexts, la estimación is very natural.

In less formal contexts, the best English translation may simply be the estimate rather than the estimation.

Yes, it sounds fairly formal, written, or technical.

That is mainly because of:

• de no ser por instead of the more everyday si no fuera por
• la estimación
• the slightly marked word order empeoraría el rendimiento

A less formal or more straightforward version would be:

• Si no fuera por la estimación, el rendimiento empeoraría.

Same meaning, more transparent structure.

Yes. The structure itself stays the same, but the main verb changes depending on the meaning.

Examples:

• De no ser por ti, no estaría aquí.
  If it weren’t for you, I wouldn’t be here.

• De no ser por la lluvia, habríamos salido.
  If it hadn’t been for the rain, we would have gone out.

So de no ser por can refer to present or past hypothetical situations.
The time reference comes mainly from the rest of the sentence.

Yes. That is an excellent replacement, and for many learners it is easier to understand and produce.

So these are near-equivalents:

• De no ser por la estimación, empeoraría el rendimiento.
• Si no fuera por la estimación, el rendimiento empeoraría.

The second version is often easier in conversation.
The first version is more compact and somewhat more formal.