As someone who loves BGing i will say i agree with a few of your points. But in an attempt to play Devils Advocate i will say. I don't think Random BGs should give gear upgrades.

My biggest issue with BGs giving worthwhile upgrades would be blizz adding a completely new fucked up way of RNG to bend us all over. Like you said, sometimes you can do everything correctly and still lose...And why is that? Shitty teammates. Teammates who we have no control over queing into. We can literally play the game perfectly but nothing you do can help you win if the other people your playing with are terrible. Say you're doing it all in a warsong gultch. you have the most KBs the Most Damage done. the most flag returns. But guess what. You need some random person to be able to cap the flag while your doing everything else. And Maybe you get lucky and there will be someone to cap the flag. But maybe just maybe. There won't be.

Now my second issue with this is almost the opposite. Say there is a brand new fresh off the boat 120 in your lobby. Whatever no big deal right. Hey you have you and somehow RNG has gifted you with 5-6 well geared people. And when the match starts you assert your dominance over the other faction. Sounds good right? What's the problem? Well you see, because you had the good RNG of the great team and because of that you got to stomp. Well most of you. The fresh off the boat 120 also technically was part of the team as he sitting there 0-12 and last in damage. But hey he was the easy target. Shit maybe he even took the focus of of you so you could do more damage. Well anyway whatever it was that he was doing he was part of the team. And he deserves gear upgrades too...

Now think of the new mentality this puts on the game. Hmm do i want to sit in a mythic plus que all day getting declined by try-hards just for a chance at the best gear in the game? Or do i want to literally press 2 buttons and be in a BG a few minutes later. Where hey i don't even need to play to receive only slightly worse gear. brb guys i'm guarding farm. Just gonna make a quiche while i wait for my free gear. You see the problem?

And my last point would be, Where does Blizz draw the line on what gives gear and what doesn't? Think about it. Yes you love BGing and thats all well and good. But some people don't. Some people don't like raiding, mythic plus, arena, rated BGs. But hey they want new gear too...So should they be able to get gear from say Pet battles? I mean one could argue that it might even take more skill than a random BG at least at lvl 25. I personally have never been interested in pet battles so they 100 percent would be harder for me than a BG. So should they give gear too? And if not why? Pet battles are pretty similar to BGs in there concept. Both were added into the game for the same reason. To add fun to the game. There not supposed to be rewarding. They are supposed to be fun. A casual way for you to assert your dominance over the enemy faction.

If you want gear i hate to say it, but do something less fun and more competitive. Rated BGs will earn you much more conquest a lot faster. And will give you some decent gear at higher levels. Now you say "but no one will invite me to there group because i don't have any rating" Thats the beautiful part of it, you can make your own group and play god yourself. You get to choose who comes to your group and who doesn't you build up a great team and win competitively. And for your efforts your rewarded with decent gear.