For me, the key issue with the balance in the game are aspects and legendary items. Their power accounts for half of the success (and with the PTR, the other half is tied to paragon and glyphs, which unfortunately leads us down the path of Diablo 3—it’s been done before and wasn’t well-received).
Migration of Aspects:
In my opinion, aspects should be removed from weapons, and each class’s skill tree should have built-in options for every spell where aspects could be integrated. What do I mean? We have the skill tree, we choose a skill (max 1 level), then we have (like now) 1 passive skill to choose from. After that, we can pick 2 additional passives (we choose one), and from that point on, we get 6 additional passive skills (we can select up to 3), which modify the spell just like aspects do. In the middle, there’s a socket for a rune that must be dropped, and this rune works like a unique aspect. (The points in the pool required to allocate are the same as now, but we gain more options for expanding builds or creating combinations.) For ultimate abilities, it works similarly, but here we can have a rune that unlocks a new paragon board to choose from (a pool of runes with additional paragon boards). For passive ultimate skills, we can choose from 3 different passive skills (acting like aspects) + 1 rune slot, and just like with ultimate abilities, we could also have a rune that grants access to an extra paragon board. It’s up to the player whether they want to invest in more than one ability, expanding the number of rune slots, or focus on one, gaining power through other passive skills from the tree. Runes could drop from a certain world tier, be tradable, and based on rarity, correspond to legendary, unique, or uber unique aspects.
Items:
Instead of aspects, they could have a pool of additional effects, such as for legendaries: x% increased stats on the weapon, +x levels to spells using rune sockets, equipment + x slot for a gem/rune word, and uniques could be tempered 1x, plus an additional effect like +x generating offering—a condition required to activate the item, which no longer requires an offering rune to activate the rune word and has the same pool as legendary items. Uber uniques could have 2 additional effect slots + can be tempered 2x. Rare items could have the same pool of effects, like being tempered x times, an extra slot, etc. In addition, the item pool could include effects like +x% damage (insert any type of damage), for every x (5-50) stat points.
With these systems, devs would have more flexibility, and we as players would have more options for playable builds, synergies, and mixing with other skills. Glyphs need a rework, because right now, too much of the character’s power (70%) has been shifted there unnecessarily. The current system of monster power in Torment 4 sets the threshold for the power level a character needs to function there (similar to Diablo 2).
Scrolls:
They should add scrolls that can be dropped from Legions, Goblins, WB, and PIT that can be used on NMD sigils. Scrolls could drop in different rarities, from common to uber rarity, and depending on the rarity, you get +x% drop rarity, +x% drop quantity, and (like in PoE) depending on negative stats like +x% HP for monsters in the dungeon, you get extra +% rarity and quantity (the better the rarity, the greater the challenge and more negative affixes, but at the same time a higher chance for drops and more items). Uber unique scrolls could guarantee a 4x great affix, or spark drop chance.