I rationalise elves' slowness at doing stuff firstly as a side effect of their physiology, and secondly as an effect of their culture.
Physiologically it stems from their extremely capable senses and excellent motor control - elves are fit, dexterous, agile and keen-eyed - practically they have near-perfect coordination and mastery over their bodies, which they then try and apply to everything else they do. They can't be content with merely being "good enough" at anything, they have to know it and master it totally.
An elf learning maths, for example, would master addition, subtraction, division and multiplication before moving on to even the most basic algebra.
A human meanwhile wouldn't give two shits about being able to multiply sets of four digit numbers together.
It means that for a human to be good at something they don't have to be as obsessive as an elf would to reach the same level - they'll take shortcuts, accept principles on face value etc., but the end result will be the same.
It also explains some of their arrogance - to them other races seem clumsy and unskilled. Like humans would see a toddler. The rest of it is them just being dicks though.
Perfectionism is the hallmark of elves - it's why they take so long to do anything, because they will only do it perfectly. Which takes ages, but hey, they have the time. But perfection is stressful, and that brings us to elven society.
Being perfectionists, and being seen to be perfect.
Elven society is all about maintaining appearances and meeting expectations. You are free to do whatever you want, within reason, but peer pressure and cliquishness is ridiculously overpowering, and image is everything. Keeping up with the Finwes is all important - have you been seen at the right parties, have you read the poetry that's in vogue at the moment, are you wearing this season's clothes?
And while doing all that you must stay perfect at your chosen profession, because perfectionism is the done thing.