Nargott
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Let me provide some examples regarding magic. Take Light magic, for instance. In the old WGE 3, most of its spells (Stone Skin, Haste, and Bless) were short-term. This is clearly a mistake – for the "Aggressor" archetype, all spells should have the option to be long-lasting, without requiring a high Magic skill. Currently, there's nothing for him to play with – only Dodge and Bless are long-lasting.
The correct design for Stone Skin/Haste/Bless is to have durations of 1/2/3/4 rounds (depending on the skill level). In this case, an "Aggressor" can still use them in the short term without investing in the school, but a "Warrior" can utilize their full power in the long term by maxing out the Light skill.
Also, a good solution for Stone Skin/Haste would be a direct dependence of the effect's strength (not duration) on the Magic skill, because this is what would allow an "Aggressor" to further increase the tempo of their short-term spells.
As for spells that are inherently long-lasting, like Dodge and Bless, the duration could be 2/4/6/8 rounds (depending on the skill level). Since these are weak spells, there's nothing wrong with them lasting the entire battle and not requiring the player to recast them periodically.
Added 19 minutes later
Or, let's take Chaos magic. The correct design for Chaos spells is to have a maximum dependence of low-level spells on the Magic skill, while keeping their mana cost low. This is because the "Destroyer" will use Magic to increase his tempo. However, for high-level Chaos magic, the dependence on Magic should be reduced, because such Chaos magic increases in tempo due to Knowledge (the ability to constantly cast powerful high-level spells).
In short, if Magic Arrow deals damage of, say, 10 x Magic, then Earth Shock should deal damage of, say, 100 + 10 x Magic (the multiplier for Magic is no higher than for the cheap arrow, but additional power is provided by a constant value).
With this approach, Magic Arrow remains competitive with Earth Shock for almost the entire game, because with a sufficiently high Magic skill, the relative difference between these spells decreases, and the ability to save mana remains crucial (Magic Arrow is almost free, unlike the expensive Earth Shock). However, with a low Magic skill, it's worth investing in high Knowledge, which will allow you to cast powerful high-level spells without a high dependence on Magic.
Take the Dark Knight, for example. One of his racial perks, Arcane Wave, is specifically designed to increase the power of low-level, cheap spells, giving them preference. But in the original game, the damage formulas for Chaos magic (as well as the mana cost policy) are incorrectly implemented, which means that low-level magic will never be interesting to him, and the Dark Knight is forced to simultaneously increase both Magic and Knowledge in order to spam enhanced high-level spells, i.e., to use the skill not for its intended purpose, but in spite of its shortcomings (obviously, forcing him to pay twice as much for already expensive spells is a mistake and a flaw in the game).
On the other hand, exceptions are permissible in the form of spells that are both expensive in mana and highly dependent on Magic (and, by the way, only Meteor and Earth Shock fit this description, as they are not boosted by perks). But most spells should follow the principle that it is wrong to force the player to increase both Magic and Knowledge at the same time, because this only narrows his choices. For example, an "Aggressor" only needs Attack; no one forces him to increase Defense at the same time (which is situational – it's critical only against other "Aggressors" and useful against "Warriors" using spells, but much less so than Attack).
The correct design for Stone Skin/Haste/Bless is to have durations of 1/2/3/4 rounds (depending on the skill level). In this case, an "Aggressor" can still use them in the short term without investing in the school, but a "Warrior" can utilize their full power in the long term by maxing out the Light skill.
Also, a good solution for Stone Skin/Haste would be a direct dependence of the effect's strength (not duration) on the Magic skill, because this is what would allow an "Aggressor" to further increase the tempo of their short-term spells.
As for spells that are inherently long-lasting, like Dodge and Bless, the duration could be 2/4/6/8 rounds (depending on the skill level). Since these are weak spells, there's nothing wrong with them lasting the entire battle and not requiring the player to recast them periodically.
Added 19 minutes later
Or, let's take Chaos magic. The correct design for Chaos spells is to have a maximum dependence of low-level spells on the Magic skill, while keeping their mana cost low. This is because the "Destroyer" will use Magic to increase his tempo. However, for high-level Chaos magic, the dependence on Magic should be reduced, because such Chaos magic increases in tempo due to Knowledge (the ability to constantly cast powerful high-level spells).
In short, if Magic Arrow deals damage of, say, 10 x Magic, then Earth Shock should deal damage of, say, 100 + 10 x Magic (the multiplier for Magic is no higher than for the cheap arrow, but additional power is provided by a constant value).
With this approach, Magic Arrow remains competitive with Earth Shock for almost the entire game, because with a sufficiently high Magic skill, the relative difference between these spells decreases, and the ability to save mana remains crucial (Magic Arrow is almost free, unlike the expensive Earth Shock). However, with a low Magic skill, it's worth investing in high Knowledge, which will allow you to cast powerful high-level spells without a high dependence on Magic.
Take the Dark Knight, for example. One of his racial perks, Arcane Wave, is specifically designed to increase the power of low-level, cheap spells, giving them preference. But in the original game, the damage formulas for Chaos magic (as well as the mana cost policy) are incorrectly implemented, which means that low-level magic will never be interesting to him, and the Dark Knight is forced to simultaneously increase both Magic and Knowledge in order to spam enhanced high-level spells, i.e., to use the skill not for its intended purpose, but in spite of its shortcomings (obviously, forcing him to pay twice as much for already expensive spells is a mistake and a flaw in the game).
On the other hand, exceptions are permissible in the form of spells that are both expensive in mana and highly dependent on Magic (and, by the way, only Meteor and Earth Shock fit this description, as they are not boosted by perks). But most spells should follow the principle that it is wrong to force the player to increase both Magic and Knowledge at the same time, because this only narrows his choices. For example, an "Aggressor" only needs Attack; no one forces him to increase Defense at the same time (which is situational – it's critical only against other "Aggressors" and useful against "Warriors" using spells, but much less so than Attack).