Its not my logic, it was the unstated reason CG did it. Because before people would focus on just the 1 meta arena squad and ride it for months. Then gac came and you suddenly needed like 10. Even in kyber you only put 3 fleets on defense and need 3 for attack.
The main reason your idea shouldn't be used is because top 50 fleet arena is almost a totally different game then top 500. With some exceptions for really crazy shards. I'm in my shard chat but still sometimes have to climb from the 20s and I do arena battles every day and sometimes get knocked back by outsiders too. Why should someone ranked 500 who's 2 metas behind or doesn't consistently play get the same rewards as me? Thats just as entitled as anyone else.