Players tank due to lack of participation, I am usually in K3 but recently dipped to A1 when I struggled for time. If players dip as far as Bronzium then they have lost a lot of rewards on the way and to maintain. They can not stay there when winning every match.
There is a noticeable difference between A1 to K3. A1 to K5 is hardly different in rewards but that makes sense as you just got promoted from A1 to K5 between seasons. You now need to climb up Kyber for better rewards. You are experiencing difficulties in K5 and many players go through a phase of promotion and relegation for a while due to the step up in squads required. The rewards average out and you do not lose out by being promoted to Kyber but it lets you develop new strategies and identify holes in your roster for more success in Kyber.
I think the tournament rewards should be the same. I put relatively the same effort into an A1 match as a K3 match. I just had to full clear in A1 but in K3 it’s more efficiency or most zones. The additional rewards is covered in the daily and season payout.