I've not read the many other posts in here so this may be repetitive but these are my ideas on arena fixes:
1) Attacking and defending
It's too difficult to judge whether you are going to win given the current state of the arena and how difficult it is. So when you attack, you should only lose half of the points that you would get if you win. On your defense team, you should gain 1 medal per defense victory because it does take effort to place a team that can withstand someone manually playing with access to all of their champs.
2) Available ranks
This happened to a game of mine (Rocket League). The ranks became too saturated with good players. They changed the ranks to have 5 possible ranks (bronze, silver, gold, platinum, diamond, champion). They added 4 sub ranks to those like you have and then added divisions beneath each sub rank. This spread out the competition and allowed for better progression and more even competition. Your base is huge and arena needs to adjust to that with its available ranks. People in Gold are overflowing into silver and silver into bronze. This fix would expand the arena for all players.
3) Speed interference
Right now, only two ways exist to counter the speed meta. Either you have Tormin or S-tier gear for a defense/resistance team. As progression is an issue, obtaining Tormin is more likely and more effective. You need to either introduce or rework current champs with passives that counter the turn meter abilities. Another legendary with a similar ability or some epics with slightly less intense abilities would be nice. Example would be WarChief. Make his A2 an AoE with an 80% max chance to provoke. Add a passive that activates the A2 anytime enemy team increases turn meter or decreases yours. Probably would lower the provoke chance but it's an idea.
4) Attack/Accuracy vs. Defense/Resistance
This is more of a bonus idea but simply put, make defense and resistance scale more strongly against attack and accuracy. This could bring the tank meta back or other variations. This "whoever is faster wins" is getting quite boring. Arena matches are a lot more fun when it lasts longer than 15 seconds.
This may fall on deaf ears and these changes will probably never see the light of day. Apologize for sounding like a broken record if I have echoed others concerns but here you go. Cheers!