"I don't mean that Merriweather Post Pavilion marks the decline as in it's inferior to earlier indie pop"
But that's exactly what a decline is, and you said that the album IS the decline, not that it "marks" it. It's not as if this is their debut record; shouldn't one of their prior albums have "marked the decline"? And since you say it's not actually a criticism, why use it as the summary?
As others have said, faulting someone for innovating with the tools is absurd at best. Doesn't matter if they're stringed or electronic, they're all just waveform generators.
Album Rating: 4.5
The mistake you made with this review is the mistake Pitchfork has continually made for over a decade, leading many to see their reviews as unreliable. Instead of discussing the album as a standalone work, or even within the context of their discography, you chose to analyse it as a segment in some superficial chain, branding it with the vague label of "indie pop" and deciding it represented the decline of this superficial genre.
That label really does not apply to this album, the fact this album exists so independently of other music being made right now (including that labeled as "indie pop") is why it is the breath of fresh air it is. This album is such a departure from a lot of alternative music being made at the moment, to anchor it to a contrived genre that was in decline long before this album materialised ignores the many merits it has.
And the few criticisms you made of it as an actual album (rather than a signal fire of indie pop's demise) are weak and hugely subjective. Of course all music is subjective, but these felt much more along the lines of "personal gripes" than "glaring flaws." Like them juxtaposing elements of electronic music with music generally considered more "organic" is not a glaring flaw, it is an attempt to mine from both sides of the fence, an attempt the majority of people view as highly successful.
As coherently written as this review was, it sounds like you simply don't like the album and are having a hard time justifying that, or going against the general consensus is something you enjoy doing.