FireLance
Legend
I think one of the easiest ways to ensure that spells scale with level and ensure that spellcasters don't eclipse the non-spellcasters is to give the spells fixed effects depending on spell level. A 3rd-level fireball doing 5d6 damage, while the 9th-level version doing 17d6 damage is a good example.
Similarly, invisibility was stated to grant a fixed Hide DC in one of the supposably leaked playtests. Presumably, remaning hidden from higher-level and more perceptive opponents will require higher-level versions of the spell.
In the case of knock, I could allow the spellcaster to open a lock of a fixed difficulty. Depending on how 5e treats locks, it could be DC 17 for the 2nd-level version, going up to DC 31 for the 9th-level version, or the 2nd-level version could open Normal locks, the 4th-level version Hard locks, the 6th-level vesion Master locks and the 8th-level version Grand Master locks. This means that if a wizard wants to open the locks he is likely to encounter at his level, he will have to prepare knock is a high level enough spell slot that it is actually a significant trade-off for him.Knock- second level- the spell creat a golden magical key that can be used to open locked doors up to 1d4+1 times, the key will disappear after 3 hours. Spell focus - a key worth 50 GP, the key have a 50% chance of disintegrating if all the spell charges are used.
Similarly, invisibility was stated to grant a fixed Hide DC in one of the supposably leaked playtests. Presumably, remaning hidden from higher-level and more perceptive opponents will require higher-level versions of the spell.
For divine power, I doubt the spell would outright grant the attacks of an equal-level fighter. Instead, the 4th-level version might grant the attacks of a 5th-level fighter, the 7th-level version might grant the attacks of a 11th-level fighter, and the 9th-level version might grant the attacks of a 15th-level fighter.Divine Power - 4th - You gain the attacks of a fighter of your level
Divine Power - 5th - You gain the attacks of a fighter of your level and a +x divine bonus to strength.