I grew particularly fond of my Arcane Trickster who shot spells through his gun. + 10 initiative, so always went first. Gave every party member a flaming weapon and casually did 12d6 damage the first round. Was fun.
As wild as the OP build is, as a GM I would consider this to be a serious abuse of the rules (regardless of it's legality/illegality). Remember that any munchkin-level tweaking you can create can also appear in the world. If this was happening in my campaign, I would create 12 of these Songbirds of Doom to come chase your party down :P
A good GM should adapt his adventures to make them challenging to his players. And he should interpret the power levels of the characters the players build as an indicator of the challenge levels they want from their GMs. But one should hesitate to dismiss creative and powerful character builds as being abusive to the rules. Character building is an art. People put a lot of creative energy into their characters, and a good GM should not just stomp on their players' artistic visions.
I agree with you for the most parts. As kind of the permanent GM of our group I can tell you that yes, theory crafting and building characters can take a long time. But filling a world with new and interesting things to explore, with a logical storyline, something interesting for all the players and also keeping everything balanced is a real time-consuming. I honestly hate it when one of my players jumps onto google: "Pathfinder insane killer build OP" and just takes that build and tells me that he spent a lot of time in designing it, and I should respect his ideas (argument came up more than once, one time even with 3 of the 5 players at once).
I have new players coming and going in my group and I tell them every time: "Don't worry about not having the most insane character build ever. Just build something you like to play and something with a lot of backgrounds." If people arrive at session 0 and join the table and they start talking about how his character has this amazing story behind him, but he doesn't even know what class he is; that brings tears to my eyes. We are telling a story. We all add to it. No one likes a story where 1 guy is fighting for his life to survive and his friend who is the same level, flies in like he is Superman and 1 hit kills 6 bad guys per round.
Of course, I also have players who don't like the insane background stories. They like to crunch the numbers, building the best there ever was. But if the players squeeze every rule to get the tiniest bonuses, then I will do the same. If you just build out of story perspective and you spend a lot of rounds doing fluff stuff, I will be more slacking on the rules.
And the group likes it. Everyone gets his satisfaction. Story guys get a story, the "artists" get the Michael Bay dynamic combat and lots of detail to work with, and the number crunchers get their satisfaction of getting stuff done.
TL;DR Give the players what they want from a game, but respect it that when you might be having fun with your op character, you might take the fun away from other players or the GM
Fun Facts! Assuming you started with a 20 strength, and placed your stat ups until at least 24 strength, then added a +6 strength belt, your rage will boost you up to a 38, which is a +14 mod. You stroll up to a Iron Door with its 10 hardness, 60 hitpoints, and strength break DC of 28 and scoff. You could shred this with your +74 strength check, but instead you decide to burst through the wall right next to it (at a mere +67)! <Queue guitar riff> Suddenly you Perform Oratory "OH YEAH!" and force your opponents within 20 feet to make a DC 30 fort save or be stunned, and those within 10 feet to make a DC 34 reflex save or take 1d4+8 damage as totally gnarly shards of hewn stone fly into them. BUT WAIT there's more! If your stupefied opponents are not stunned you launch into a terrifying air guitar...