I've been picking everyone's brain about a shifting issue. One time my new bike RD won't upshift. The next time, it won't downshift. Someone mentioned to check for anything causing friction. I disassembled the shifter cable from front to back, and all looks well, but could it be that the cable housing going to the derailleur itself is too short, with the result being that the final bend is too sharp? Take a look and tell me what you guys think?

IMO the rear loop length looks fine. It's not the length per se, it's how it aligns entering the RD fitting, and it looks straight on, which is correct. Howeer, I see you have interanl routing, and these can be (don't have to be) prone to friction at places like the bend in the BB. If there's any place you can access bare wire pull it away from the frame like a bow string and observe if the RD move smoothly or in small jerks. Also shift to any gear, then use the lever to shift half way to the next (not enough to latch the click) and let go and see if the RD crisply returns to correct trim. If so, it's fine, if not, you have friction someplace along the line.

Have you had the derailleur hanger alignment checked? Whenever I encounter a shifting problem that doesn't respond to normal tuning that's the first thing that I check. Most of the time, that's it.

Looks all shiny and new.

Try this: shift to the smallest cog, then without pedalling, shift back a few clicks, which will pull on the cable pretty hard (but don't do it as hard as you can, maybe 1/4 of that). Now pedal forward to take the tension off the cable, then release the shifter all the way again so you're in the smallest cog once more.

Now, shift a click back up the cassette. Don't freak out if the chain doesn't shift onto the next cog; that's a good thing because it means you've bedded in the cable system (mostly the housing ferrules, maybe poorly-done under-tape routing too). Just wind out the derailer's barrel adjuster until the chain shifts onto the next cog, and keep winding until the pulleys are centred below the cog.

If the problem's been addressed, now you can compare the shift up and down the cassette and fine-tune to equalise the response.

If not, it's time to check the hanger alignment, and if that doesn't sort it, go over the cable system with a fine-tooth comb, removing as much friction as possible.

...Now I take another look at your pics, I can see a kink in the cable before the pinch bolt. That's not cool... cable kinks add springiness to the system, something you can ill afford on Shimano 10s.

Any kinks like that need to be straightened with pliers, and if you have anything like that inside the housing the cable should be replaced.

Also, you should twist those loose strands onto the end before they get bent and you can't.

You might try playing with the B screw adjustment. i'd try backing it out as much as you can without having the guide pulley hit the cogs.

I installed a Tiagra RDER on my hybrid, thinking it might shift my 12-23 cassette a bit better than the original Altus that came on the bike. Original cassette was an 11-32?
I had the same problem as you. I put the Altus back on and it's definitely better shifting. Doesn't make sense, but it is what it is.