The thing is I appreciate your convictions and personal beliefs, and I don't want to offend you by disagreeing, but at the end of the day this has already been studied and relevant conclusions are well known.
Why is hit (usually) better than
Short answer: Combat Potency
Medium answer: white hits are like 50% of our dmg in raids, if you're only at 9% you're going to miss out on a lot of raw-white dmg. Every white MISS you see on your screen could have been a normal 200/500 hit, a 400/1000 crit, sword spec proc, combat potency proc, wf mongoose / poisons / vial proc etc
Long answer: AEP values! People have already worked out a system to digest stats of an item to figure out the overall benefit it will have in regards to your DPS. Before your white hit is capped each agility point roughly translates to 2.3 AP and each 1 point of hit rating equals roughly 2.5 AP. These are not fixed values and they tend to fluctuate depending on your gear and buff situation, but its an OK guideline for a new rogue gearing like the OP.
However, following the above AEP values, you are indeed correct in your assumption that losing 15 agi for 10 hit rating is not worth it, as you end up losing roughly 9 AP! You're also correct that hit is not a magical number that needs to be capped out - it's all relative to one's gear / gem / enchant / buff composition.
A comment that I thought brilliantly summarised this from Rogue Discord: <i>There will be breakpoints where agi starts to become more appealing than hit and vise-versa. If you are at 9% hit, agility can't even come close to making up the damage for the loss white attacks/sword procs/potency procs. But swing that the other way, even at 71 hit cap, agility starts to raise in value because more attacks are landing, therefore increasing the overall benefit from agility.</i>
Capping the white hit is still super important. Let's forget the AEP values for now, and just focus on the simple logic: more hit rating = more white hits landing = more combat potency procs <- this alone is one of the strongest arguments for why hit cap is rather important. This proc is soooo good, but it cannot be compared to the raw AP / Crit that agility provides, it just works differently!
Finally, not being white hit capped will reduce the power of your other stats such as attack power and crit chance. Say, you have 33% crit, but it doesn't mean that you're actually critting 33% of all your hits. Crit chance is rolled out after you've landed a strike, and since you're not hit capped, about 20% of your white hits are going to be missed. Therefore your 33% only applies to the 80% of your white hits - reducing the overall benefit of your crit. Therefore eliminating dodges / parries (expertise) and misses (hit) are THE two single most important stats in terms of increasing our dmg output. Again, it doesn't mean that we want to chase hit rating only and ignore other stats, but you need to consider the bigger picture of what NOT having that extra hit will mean for the overall boss fight.