by far=way (too much)??
There's a definition of adverb 'way' in the Collins Cobuild dictionary that
"[ADV](emphasis) You can use way to emphasize, for example, that something is a great distance away or is very much below or above a particular level or amount."

And there's a definition of 'by far' that "by a very great amount; much
'1.This is by far the best painting / 2.This is the best painting by far'"
Then, do the sentence 1, the 2 mean the same thing as
'This is way too much the best painting.(1)'.
'This is the best painting way too much.(2)'?

Question

by far=way (too much)??
There's a definition of adverb 'way' in the Collins Cobuild dictionary that
"[ADV](emphasis) You can use way to emphasize, for example, that something is a great distance away or is very much below or above a particular level or amount."

And there's a definition of 'by far' that "by a very great amount; much
'1.This is by far the best painting / 2.This is the best painting by far'"
Then, do the sentence 1, the 2 mean the same thing as 
'This is way too much the best painting.(1)'. 
'This is the best painting way too much.(2)'?

Answer

"by far" means "to the most extreme degree"

a) That car is the most expensive car I have ever seen. I have never seen a car that is more expensive than that one.

b) That car is /by far/ the most expensive car I have ever seen. No other car that I have ever seen comes close to being as expensive as that one.

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"far" and "way" and "much" can mean "to a great degree" But this is not the same thing as "to the most extreme degree" (or: "by far").

So, the following three are identical in meaning:
That car is /way/ too expensive. I do not have enough money to buy it.
That car is /far/ too expensive.  I do not have enough money to buy it.
That car is /much/ too expensive.  I do not have enough money to buy it.

So, "way" can mean "far." But "way" does not mean "by far."

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Last, we have another expression "far and away," which is really just another way to express "by far," except with even more emphasis.

That car is /far and away/ the most expensive car that I have ever seen.

Answer

When comparing things you can use "by far" to express the thing that is clearly different (outstanding) from the others.  
This is, by far, the best ice cream I have ever tasted.
This is, by far, the worst movie I have ever watched.