There’s nothing wrong with shooting for a straight handstand, I’m not going to talk you out of it, but it’s not worth stressing over.
(This article does contain practical tips)
The reality is, everybody at the BBQ, everybody in Yoga class, everybody in the Crossfit Box, and everybody on Instagram, will be perfectly impressed with any kind of handstand, and may even be more impressed with pretty figure shapes (which are easier to hold).
The people who NEED a perfectly straight handstand (professional circus Handbalancers, or people who intend on mastering one-arm) are so few, so rare, they basically don’t exist as a demographic.
For most of us, balancing any kind of shape is enough to make us happy.
Going perfectly straight is quite difficult. A lot of shoulder mobility is required to have the arms in line with the spine.
Some of us are lucky, and our arms will go there without much work. Others are very tight and need a lot of stretching to get there.
In most cases, the back arch happens as compensation for the tight/closed shoulder angle. See the photo below. Also, we are stronger with the chest forward because the pecs become involved (which relieves the delts and traps). (Think how much more you can bench press than shoulder press above your head).
This will be a more comfortable position to relax into, which is why cross fit people let their legs dangle, and why yoga people opt for scorpion rather than straight.
If you do want to get straighter, you will probably need to stretch your shoulder angle open which removes the need for the back arch. Try going up into handstand against a wall, carefully lower your bum to the wall, and push your chest through so that your shoulders and upper back get a stretch.
I personally felt that the process of practising handstands gradually stretched my shoulders into position, without any deliberate stretching.
So if you’re not there yet, relax, even without stretching, you could just keep practising handstands and your alignment will improve.
If you have tight shoulders (very common), dangling one leg over your head (either straight or bent) and keeping the other knee closer to your tummy will counter-balance that shoulder angle and allow you to balance even with tight shoulders. See photos below.
For people with a good back bend, dangling both legs over your head (aka scorpion) will also be more comfortable than a straight handstand.
On the contrary. Any position where your leg weight is more towards your tummy side, (such as both knees in a tuck, or legs straight in piked position), will require even more openness from the shoulders to allow the counterbalance of the bum to work. People with tight shoulders always find tuck difficult.
Here’s something that will blow your mind. For most people, core strength is not even remotely a limiting factor. That means, if you’re working on core strength expecting it to improve your handstand, you’re wasting your time.
There can only ever be one limiting factor at any moment in time, and only improving that factor will give you progress.
The reality is, you are much more likely to be limited by a lack of shoulder strength. Building up your delts will do much more to stabilise your handstand than planks and crunches will