The Big difference between Bf5 or Bg4 can be seen below:
The below is with Bf5
The below is with Bg4
Black is trying to defend e4 square and we can see both bishop moves ultimately do that function. The question is whether or not Black should go directly to f5 and defend e4 or if Black should try to go the long way around.
‘Black has no intention of trading off his bishop for knight.
‘Black intentions with Bg4 are to annoy and provoke white into over extending.
Scandy players believe by playing Bf5 directly. It defends e4, but it doesn’t cause any weakness in white position.
Bg4 is the sophisticated way to defend e4 and try to annoy white into playing h3 + g4 which would create dark square weakness around king!
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In fact, White is not suppose to play g4!
White is supposed to play only h3 and hold g4 for later time.
The move g4 is to weakening and it gives Black counter play.
‘Usually, Strong Black players will play Bg6 on their own later in game.
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‘Everything Ibrust said is also pretty accurate.
‘White attacks the entire diagonal and in addition white uses e4 as outpost to help stage attacks.
‘Black is on defense the whole game which is why I say the Qa5 line is losing.
Engines can hold draw playing Black because they have crazy good engine defense, but most humans get crushed.
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The Qd8 line was losing same way, until this new line came out.
‘I am little nerves by it.
I’m going to have to change something - maybe my move order
You are simply ignoring BASIC OPENING PRINCIPLES in your wannabe-analysis.
Ideally, Black would love to grab some central space without falling way back in development.
So, an early ...e5 is not an option against 4.d4, or 4.Nf3 5.dxe5 against the former, or 5.Bc4 against the latter will make Black regret his experiment.
4...e5 is also bad against 5.Bc4 (6.Nf3! and an eventual Ng5 is already a big problem).
Hardly the case after the meek 4.g3, which DOES NOT PUT any direct control over the e5 square: Black has the luxury of doing just that without any sort of "punishment", and enjoy a very healthy position.
This is objectively the case, and stuff like an early ...Bf5 and/or ...Bg4 simply shows that Black is a guy who moves on autopilot.
See what an objective kibitzer says:

But hey, feel free to support your illusion. Just don't expect someone who understands a couple of things about chess to agree with you.


In the Qa5 line, I personally do not believe in the Bg4 move you showed.
I think most scandinavian players will go for the standard Bf5 move instead and go for the standard scandinavian principles. Trade off the light squared bishop for anything, and rebuild the light squares.