One of the problems I see in this game is that I’m a little unsure about what the designers want players to do with their rosters.
The very scare amount of ISO-8 that players can be reasonably expected to win imply that designers want players to focus on only 3-4 characters at a time, their ideal team and a few replacements at the most. Outside of PvE events (of which the last few have been far to difficult to reliably win ISO from), players can only be expected to win 105 ISO per match (through PvP, on average). With many of the higher levels costing lots of ISO (1500+) per level, this means that players can spend hours to level up a single character once.
However, the events seem to indicate that developers want players to distribute their ISO among many different characters. With the way each event has different characters that are either buffed or required to participate (and some, like the Heroic Modes, which limit the cast of select-able characters), it seems like the only way to do well is to make sure that you have decent levels in multiple characters to ensure that you have a character that is buffed or required at a strong enough state to participate.
This results is an unfocused game whose mechanics are opposing each other. In order to make the two mechanics fall in line, in would make sense to raise ISO-8 reward so that players can be more reasonably expected to have characters at the decent levels and diversify their teams. The current landscape almost requires players to double-down on a team of three just to avoid wasting ISO.
Another option would be to design events around the knowledge that players are likely to only have 3-4 high leveled characters. However, I believe this wouldn’t be as fun and developers have already admitted to wanting to diversify player team formations.