It only takes an hour to reach level 30. You haven't reached the grind levels.
Late on, the story only gets you one level. You have to grind for 4 levels before the next story.
There are 6 bundles. The prices are $1, $1, $2, $4, $7, $10.
The extra value becomes less and less.
None of them guarantees a 5-star gem. You have 4% chance to get a random 5-star gem.
At level 50, there is a $20 deal.
I am sure that you can finish the main story without paying.
It is the end game which requires 5-star gem.
No one knows how painful the end game is, so don't spend any money.
Not even the $1 deal.
There are lots of things require to upgrade.
They are either locked behind by a weekly raid or another paywall which we don't know about.