Grand Arena Matchmaking Is Broken — How Is 6M GP vs. 10M+ GP Fair?

At what point? Never. 

You are matched with people directly adjacent to you on the Skill Rating ladder. Period. 

Hard disagree that GP / No. of GLs should be considered. 

harvestmouse1​ has an "activity score" proposal that I like more and more every time he posts it. 

I couldn't agree more with this. Honestly, the matchmaking system has gotten to the point where it's actively killing my motivation to play the game.

What's the point of spending months, or even years, building your roster, grinding for characters, farming gear, and investing your resources when you're constantly being thrown into matchups against players who have millions more GP and several more Galactic Legends than you? I'm sitting here trying to make the best of the roster I've worked so hard to build, only to face opponents who have twice my GP and an absurd advantage in terms of available characters and teams.

People keep saying it's about skill rating and strategy, but there's only so much strategy can accomplish when the difference in roster strength is this massive. You can play perfectly, set your defenses strategically, and make all the right decisions, but you can't magically pull counters or characters out of thin air.

At this point, Grand Arena doesn't even feel competitive anymore. Instead of looking forward to participating, I find myself losing interest before the round even begins. And that's honestly a terrible feeling for a game that expects players to invest so much time and effort into building their accounts.

I'm getting to the point where I genuinely don't even feel like participating in Grand Arena anymore, and that frustration is starting to affect my desire to play the game altogether. Why should I keep grinding and investing my time if the matchmaking constantly makes me feel like my progress means absolutely nothing?

I don't expect easy wins, and I don't expect the game to hand me victories. I just want matchups where I have a reasonable chance to compete. There's a huge difference between being challenged by someone with a stronger roster and being placed against someone whose account completely dwarfs yours.

If this is what Grand Arena is supposed to look like, then I honestly have to question why I'm even bothering anymore. A competitive mode should motivate players to improve their rosters, not make them feel like all their hard work is pointless.

A competitive mode should motivate players to improve their rosters

The problem with using GP or number of GLs in matchmaking considerations is that we know - for a fact - that this system did the opposite in terms of player motivation to improve their rosters. 

I can give you a view from the "other" side...i am top dog in my bracket with 11M...opps are 1x9M, 2x7M and 4x below 6M...this is the norm these days.
I used to be like YOU long time ago...i played always vs better opps and won a lot by using skill...using the best counters, planning attack and defense and winning some when the opp did not attack.

The reason i am now top dog is actually simple...i got bored! 
So i start missing lots of GAC attacks...game would give me a loss and i would drop in the ranks. Sometimes i would play and win...but more often i would lose 2+ on each GAC just by not attacking...
Nowadays i dropped so low i win all battles i remember to do my attacks...BUT i am pretty sure a lot of players with worse rosters get wins at my expense just by doing one attack, as i often forget (or don't care enough) to attack.

FAIR...probably not...but game will reward effort and give ACTIVE and SKILLED players more wins, including vs better rosters. IF the top dog decides to play all attacks you will probably lose...but i would bet than more often than not you will get wins...and some are very satisfying, when the opp is "better".

System actually works IMHO...it can't be cheated easily...if you play well you will keep winning until all opps have better rosters. That is when you know you are in your "level"...and can only improve by getting a better roster. Been there, so i know...and yes...the "chores" are lots of fun, but will eventually bore/annoy you.

Never, ever want to go back to this system again.  So many issues with GP being the qualifier 

I agree they need an improved system. Also for less rewards I'd like to not use Datacrons. Go back to the old style no datacron battles. Tired of farming Datacrons to just not be able to get one cause of the cost of the reroll materials. Also I have heard CG has this system in place to try and get people to Buy to catch up to those higher GP levels. That just discourages me for sure. 2 and a half years ago I always was fighting like 3 to 5 mil GP higher and tended to lose a ton. If I see I am out classed, and dont have time, Ill just do the one battle for rewards and call it. Half the time any more I lose more than I when cause I work graves and sleep during the day. At times I miss getting the last hour of battles in anyways. Owell. Again, yes I agree some level of GP is needed during match making and to not jump from bottom Bronzium all the way to Kyber. Also maybe add a Beskar Teir above Kyber and have it like 7 to 10 levels in each. Open it up more, and increase the rewards. I feel the Rewards could be upped every other year or so to keep up with the Cost of So many characters needed, plus the requirements of needing Relic levels now that CG wants us to have. 

3mil gp here, first battle in GA was vs someone with 9 mil power. My second battle I got matched up with someone at 900k power. Sucks for them but i always get bullied so its time to steal this kids lunch money.

I agree the matchmaking is horrendus but how else are they going to squeeze more money out of this disney/Starwars charity bin. Complaining wont do you much just put your credit card to use and drop some money if you want to compete. (I read that in the TOS)