This tree location seems cursed - as it’s front and center to our sidewalk view and where I want a nice looking tree the most. 
First I had a persimmon that grew 1 inch and died (probably not truly hardy to our zone), an Akane apple on M26 that runted out, and now this Harko nectarine on Citation that I’m thinking about pulling. The tree doesn’t look bad, but I’ve been reading about Citation’s issues with inducing early blooming (bad for our springs), and delayed incompatibility with peach/nectarine and overall runting out. And I’ve got all my non-miniature peach/nects on Citation 
This one only grew about 12 inches, where at least my Frost and Indian Free put out 2-3 feet of growth the first year. I’m thinking I might get a bigger tree faster by pulling it and putting something on Lovell in it’s place. But I know impatience is one of my key issues, so it could be best to wait it out and see what happens. How much growth do you expect out of a peach/nect on Lovell in year one in a 6b-ish zone?
Some trees just don’t develop right. Heck if you look are a litter (sp?) of doggies some are big, some are runty, some may have a defect, and some don’t make it. I have an apple tree that refuses to prosper.
Double check that the tree is right for your environment, test the soil for nutrients, test for drainage, and quadruple your mulching with something that decomposes, not something barky. Replacing it is a judgement call, not a right or wrong thing.
Your tree doesn’t look bad. Can’t tell from the picture, but it looks like it grew normal if the number I put on your picture closer to its real growth. The problem I see is that the tree is not balanced. The left side branch took more energy than others. Talking about how much a Lovell grow each year. Well, it depends. My Snow Queen nectarine is on Lovell and is only about 6’ tall. It has been there for about 10 years. And I am very happy with its size.
I think fruit trees are a lot about patience and you sound very impatient with the plants lol, it’s fine though. I would have a hard time judging the tree so soon, it looks like it grew a lot to me, like Annie says above.
I think it is hard to keep peaches looking clean because they grow so much and so easily get diseases. Requires the owner to prune well.
I would go for asian pear or persimmon if you want something that looks showy. Make sure to fertilize the persimmon well the first year so it doesn’t just die because of transplant shock which seems often for them. You want american persimmon not asian for 6b zone. Follow this zone-cultivar guide I will link here.
You’re right it’s quite unbalanced. It had one much thicker scaffold which I probably should have eliminated. Last year’s growth is about 12 inches, the tallest dominant one maybe put on 15 inches.
Did you summer prune your Snow Queen to try go keep it at 6 feet? Or it just naturally worked out like that?
I’m impatient with lots of things, a blessing and a curse 
Yeah good point that peach inherently might not be best choice visually for that location. The persimmon I tried was Izu, which I think is an American - fuyu type cross which was supposed to impart more cold hardiness, but i don’t know that it was hardy enough for here.
No Izu is a “kaki” Asian persimmon. It even died for Richard in zone 10. So it was definitely not right for your climate.
here is the story of Richard’s Izu
Oh interesting, yeah definitely not the right choice. Dave Wilson lists Izu as zone 7-10, and OGW says it’s hardy to 0 F, but I guess OGW is grafting it onto American persimmon rootstock? Our local nursery is still ordering it to sell here…but I’ve not heard anyone succeeding with it around here.
Re: the nectarine, my concern isn’t completely that it is growing slowly - because it might just take time. It’s more that I’m questioning the appropriateness of Citation rootstock here and thinking if I should be hedging my bets with a tree on St Julian or Lovell in case all my other trees on Citation have issues with early blooming, or early decline. It’s all a long game to find out if the Citation issues are even a problem for my area, but I realize now it might have been smarter to try a variety of rootstocks in case some do significantly better than others. My neighbor has a peach on Lovell that is quite happy and one on Citation that doesn’t look nearly as good.
I followed Olpea’s advice and kept it very short before it started to bear fruits. After it started to fruit, its growth slowed down a lot. I just keep regular winter pruning. Actually, it was kept ~ 5’ tall till couple of years ago. It started to grow a new scaffold which made it taller now. I think the location of the tree helped the tree stayed short. It is on the North side of the house, and the soil is very clay. It’s a Monrovia nursery tree. I am very happy with Lovell rootstock. That location is relatively low, so in spring time when we get continuous rain, it will have water pooled there. Apparently it can handle wet feet without problem