articles - Singular Vs plural while making a general statement

I'm having a hard time understanding whether to use plural or singular while making general sentences.

Doing a bit of research I found both can be used. For example:

1. 
   

   
   

   Dogs are loyal animals.

   
   

   
   


2. 
   
   

   
   

   A dog is a loyal animal.

   
   

   
   

(Both these sentences are talking about all/any dogs in general)

3. 
   

   
   

   A child needs care.

   
   
   

   
   


4. 
   

   
   

   Children need care.

   
   

   
   

(Both these sentences talk about all/ any children in general).

Now, as for the question:

Recently, I looked up in the internet as to when is a definite article used. It says "We use the definite article in front of a noun when we believe 'the reader' knows exactly what we are referring to."

I think this statement is a general statement about the use of definite article. My first question, am I right in thinking that this is a general statement?

Second question is, what if we use 'readers' in place of 'the reader'? Will there be a change in meaning then? I'm asking this question because if this is a general statement then if I use 'a reader' or 'readers' in place of 'the reader' then it should all mean the same, i.e., all of them should be expressing 'any reader' just like the examples above (1 to 4). Right?

Another example:

(1) Banks are financial institutions where 'a lender' meets 'a borrower'.

I guess this is also a general statement about banks. So can I phrase this sentence like this without any change in meaning?

(2) Banks are financial institutions where 'lenders' meet 'borrowers'.

In sentence (1), 'a lender' expresses just one lender or any lender? In sentence (2), 'lenders' expresses more than one lender or any lender in general?