Mad respect for anyone who knows of and has seriously played Super Mario x Puzzle and Dragons.
The changes in the recent updates have made it considerably more difficult to get out of the vortex you are describing. With most content now scaling to the character (outside of Story mode) on the account that’s the highest level, a young player can scale themselves into a very deep hole quite quickly. The goal of course, is to compel that player to buy the required upgrade shards from the shop tab for Gems and Crowns.
@shmaunpq is generally correct. Starting alternate characters is the ideal way to grind the shards needed to upgrade equipment. Gear can freely be used by any character class without penalty. Each unique class can earn the “first time rewards” for clearing each Story stage which is huge.
A couple of thoughts:
Starting with Chapter 2, followers gain side quests with each new chapter. These are a good one-time source per character for extra loot. Also, at certain chapters, follower crystals can be earned, which can be repeated for each unique character class played.
Don’t worry about building a class specific set of gear for now, because you will be passing that gear back and forth between all of your alternate characters. For quite a good while, the raw stats on gear (especially weapons) will overcome the majority of the story mode until the late chapters.
“Easy” is a misnomer and is not a penalty. The level of the skirmish dungeon determines the types of shards that can drop (5+ for lesser shards, 15+ for greater shards, etc.) and has an influence on the initial rarity of loot from chests.
A “Common” level 1 gear piece leveled and ascended to Rare level 25 or Epic level 35, will have the same stats as that same piece of gear if it dropped from a chest at a higher rarity. Higher rarity drops simply skips some of the earlier ascension steps, which are generally not hard to achieve at all.
More or less, yes. Max level for a character is 50, which places “easy” mode for skirmishes and dungeons at level 30. Events start at level 40 for a level 50 character. Once fights at that level become not difficult to clear, the mandatory difficulty curve stops growing. There are higher difficulties to challenge players, but those are purely optional.
Dungeon/skirmishes are good for loot, which means shards for upgrading gear. Cycle around multiple characters to upgrade a set of patchwork equipment, passing that equipment around as needed to each alt whenever one hits a difficulty wall.
You can get slow amounts of help from the daily shop rotations (low rarity shards do not cost premium currency, and if you can clear Events, the Marks won can be used to purchases additional shards in the Rewards → Marks tab.
It will be a grind and will take time, but with perseverance, you can escape the leveling vortex and come out successfully on the other side.