Is it too powerful if it was only ever 1 Pact Spell slot, and the ability to use the ritual recharged with every Short Rest? This gives you extra 1 Pact spell slot per short rest, but rather than increase the total Pact Spell slots overall, increasing your alpha strike ability, your recovery is slowed because it occurs between fights.
Assume you are a level 10 warlock, starting with 2 5th-level Pact Spell slots at the beginning of your day.
- Cast 2 Pact Spells. (2 Pact Spells cast today so far.)
- Use 1-minute ritual to get 1 Pact Spell slot back.
- Cast 1 Pact Spell before your first Short Rest. (3 Pact Spells cast today so far.)
- First Short Rest, get 2 Pact Spell slots back and recharge the ritual.
- Cast 2 Pact Spells. (5 Pact Spells cast today so far.)
- Use 1-minute ritual to get 1 Pact Spell slot back.
- Cast 1 Pact Spell before your second Short Rest. (6 Pact Spells cast today so far.)
- Second Short Rest, get 2 Pact Spell slots back and recharge the ritual.
- Cast 2 Pact Spells. (8 Pact Spells cast today so far.)
- Use 1-minute ritual to get 1 Pact Spell slot back.
- Cast 1 Pact Spell before your next Rest. (9 Pact Spells cast today so far.)
- Decide to take a Third Short Rest or your Long Rest, depending on how your day is going.
With this change, you would have gotten 3 extra Pact Spell slots throughout the day (instead of 1), but would need smaller breaks to get them. Is that too fiddly?
This also means they would have to do something different for the Eldritch Master capstone ability. Maybe Magical Cunning can restore all your Pact Spell slots once per long rest, but not every time you use Magical Cunning?