There is a world out there where people pay 15~20% of their annual income to buy a computer

seen under a different lens: you think that an effort a person does over 3.65 days to afford a computer is expensive, while many people would have to accumulate the effort of 73 days to afford it.

You're buying a tool for your work, it will last at least 2 years, and as a developer you have almost no ongoing costs or required consumables. Comparing to many other kinds of jobs, 1% per year for equipment is nothing. If it makes your job more comfortable or faster, thinking too much to decide between 0-2% of your annual salary seems counterproductive.

large: yes, justifiable: very possibly.

I think of a laptop in the same way as a chef's knife: it needs to be an extension of your being when you are in the zone, and good tools do that. Ive had near-religious experiences woodworking with good tools and other craft types tell me they have too.

for such a tool, 1% is nothing.

A large purchase- but perhaps just small enough you can agree with yourself to let go of worry. Perpetual anxiety about theft is no way to live.

What if one only buys a laptop once every three or four years? Then it would be 1/3 or 1/4 of a percent of annual salary.

It would probably be tax deductible, depending of course on variables not discussed yet.