Hi there,
I'm sorry you're not happy with the outcome of your TKR. I'm around the same age as you, am also physically active (sports, hiking, etc.) and am now 10 months post-op. My flexion is hovering somewhere between 120 and 125, and hasn't moved for the last few months. I'm told it will improve over time, but I'm not expecting much more than 130. The joint was very compromised before the TKR and I can still feel the muscles and other components learning to function in a new way.
However.
Before the operation, I could hike on moderate ground, but only for short distances, because the pain was just too much to bear. Now, I can hike long distances - 10 miles or more - on moderate to rough hilly ground with no pain whatsoever. That, in my book, is a life-changing improvement. Pre-op pain sucked the joy out of much of my life; it's been wonderful to re-discover the pleasure of physical activity. Also, my gait has become normal again, since I can straighten the knee fully (couldn't do that before), with the result that the aches and pains in the hip and knee of my "good" leg have gone away.
There are work-arounds for most of the inconvenient aspects of having less flexion. I can't climb a rock face, but I can (and do) run, jog, walk long distances, ride a bike, roller skate, compete in agility trials with my dog and ski (carefully) on moderate slopes. I can get up and down ladders easily (I put Christmas lights around our house's gutters this year). I can't step down from a high stool, but I can step down from a normal chair and I have a 3-step mini-ladder that I use when I need a higher reach - for example, to change the filter in our ceiling vent (it's also safer than a high stool). As you point out, you were limited before the operation by pain; now you're limited by flexion. Before, you were able to work around the pain. Maybe you can work around the flexion now.
My surgeon told me before the operation that he tended not to operate on younger patients (under 70) if they were very active because they expected too much and were often dissatisfied with the results. It's always seemed clear to me that a metal joint could never be as flexible as a healthy bone joint, but since metal joints are put in to replace unhealthy bone joints ...
When my dad was dying of cancer 20 years ago, his Macmillan nurse (in England) told him: the trick to living with this disease is to learn to enjoy the life you have now, and not fret about the life you wish you had. It was wise advice and I've followed it in other situations since then, including my TKR.
I wish you all the best!