Maybe his skillset is in a different field? I can't fix a car, but I'm pretty decent at most basic home improvement things. I'm not a coder, but my houseplants are healthy.

Just about everyone has things they're good at, and things they're not. Just because someone doesn't have the same interests or abilities that you do doesn't make them less of a person.

Wood conditioner should be put down before stain, to help even out the stain's penetration.

If it were me, I'd sand off the progress you've made so far and reapply. If you don't care about the finish, then don't bother, but it's something that would bother me if it were my own project.

I'd start with an 80 grit, bring it down to bare wood, then work my way up to at least a 220 if it's something my skin would be touching on the regular. Then, stain it the colour you want with a regular stain, finish it off with a spar varnish (if you're going to have any liquids on the desk, like your morning coffee), to prevent water damage in the future.

I can't say I've ever used a roller for finishes, but I'd probably hazard a guess to say it's not the best way.

Personally, I've used a lint-free cloth or foam brush for applying a polyurethane finish, and regular brushes for stain.

Those vertical strips look to be the actual grain of the wood though. What grit did you finish on when you sanded? If sanding isn't the cause, then what about applying a wood conditioner first?