I think pretty much all 3-in-1 edits do this including mine (which just got approved!).
The only times it strays from Bilbo are:
-When Bard fights Smaug, we have to step away from Bilbo
-During the lead up to the final battle (and during it), Bilbo starts to get overshadowed by these huge events: armies coming together, alliances being formed, Thorin's arc has to be wrapped up, fighting breaks out, and then he gets knocked out.
-When Bilbo gets separated from the company, we take a few looks at the rest of the Company (which makes sense, seeing them get imprisoned by Elves/seeing them captured by Goblins)
Over 4 hours of footage of sideplots and sidecharacters have been entirely removed, the White Council, Radagast, Sauron, Thrain, Tauriel, Legolas, Azog/Bolg, etc.
That said, my edit is still just about 4 hours, similar to Rotk runtime. Might feel too long still, but with all my editing goals that was definitely the right move. If you want something shorter, that's still possible but I really only think you could push it to 3.5 hours before you lose a lot of good moments for the sake of runtime.
You also mention the emphasis on Thorin, which I totally agree on. It was great to be able to reduce the dragon sickness plot, both by removing entire scenes of him going psycho, and also doing smaller characterization trims to tone down his arc (he's not lashing out threatening to kill people, he's not yelling crazily, not turning into Smaug's voice). These changes bring the story back to Bilbo by reducing the focus on Thorin, while also making sure that Thorin's arc in itself is not over the top and now feels more grounded, a prideful stubborn King, not a deranged sick King. Gives him more agency too, it wasn't a family sickness that he was subject to, it was his own flaws that led him to his lowest point.