I assume the double-preparation requirement is to offset the +1?
It is an attempt to balance the power of the ability in and of itself, not just related to the +1, though it is certainly arguable whether that is necessary or not.
I think that it is problematic as written. Let's say I dip two levels of a class like sorcerer, then continue 18 levels as a wizard. I'll never be able to use this feat since I can only swap my sorcerer spells when I level up as a sorcerer, which I'm not doing. I need to take more levels of sorcerer just to benefit from this feat.
Yeah… it is a bummer, for sure, but not sure it’s a big deal…? A few thoughts on that:
1. First, just a quick look at the applicability of this feat to that build, a Sorc2/Wiz18 does (eventually) get access to 9th level Wizard spells even without this feat. So for this build, that feat’s main attraction would be to prep the spells earlier, but not to get any that they could not ever get by level 20. It would be good, but not necessarily the main target demographic.
2. Second, regarding the overall design intents of 5e, I assume that classes which have more limited spell swapping mechanics are this way for balance reasons. It is part of a Wizard’s power to have the ability to swap spells from day-to-day (and even during the day once they get Memorize Spell at 5th level). We could make spell-swapping easier for all classes, but then that is essentially a whole other ability that this feat would grant in addition to the ability of higher level prep. And while it’s true that the feat as I have written it in the first version above helps some class combos more than others (and we could argue therefore is unbalanced), if we gave enhanced swapping mechanics as part of the feat that too would help some class combos more than others (and therefore still be unbalanced, but in a different way). It’s a tough nut to crack…
3. Regarding the mechanic of needing to go back and re-level-up an old class just to swap its spells… I think it feels thematically appropriate. This kind of character is truly straddling different fields of studies, and they feed off of one another, but that positive interaction requires continuing to fuel both buckets with further efforts. Also, from a balance perspective it provides more benefit to builds that are more evenly split between classes, which we could argue under vanilla rules are the builds which are most underpowered, whereas it provides less benefit to builds that are heavily skewed towards a single class. Going back to the Sorc/Wiz example… a Sorc2/Wiz18 or Sorc3/Wiz17 is actually quite good even under vanilla rules, and doesn’t necessarily need a big boost. Whereas a Sorc10/Wiz10 is probably considered by most optimizers to be quite a bit weaker, so it’s not a bad thing if the feat naturally boosts that weaker build more than the one which is already strong.
That being said, I’ll take a stab at writing the feat in a different way, just so we can see what that would look like…
Combined Studies (v0.2)
Requirements: Spellcasting feature from two or more classes
Flexible Learner. Whenever you gain a level in any of your spellcasting classes, you can exercise the ability to swap prepared spells in all of your spellcasting classes. If a given class lets you swap a fixed quantity of prepared spells when gaining a level, then you can still swap only that specified amount for that specific class.
Unified Magic. You have dabbled in various kinds of magic and discovered commonalities between them, allowing you to approach the abilities of those who specialize in a single path. For spells which are present in the lists of more than one of the classes granting you the spellcasting feature, you can sum up the levels in those classes (considering fractional levels for the half-caster and third-caster classes) to determine whether you are capable of preparing those spells. Doing so is more taxing than preparing a spell using the levels of a single class, and you therefore need to allocate a prepared spell in each of the classes which are contributing necessary levels. You can choose which spellcasting ability to use for that spell from those of any of the contributing classes.
Now that I think of it… it might not be bad to make those into two distinct half-feats… you had originally said maybe this ability should be multiple feats, and yeah, maybe it should be. This would be one way to do it. I could see some builds wanting to benefit from just one or the other of these abilities.
BTW, I am thinking to add a clause specifically for the Bard’s Magical Secrets saying that spells gained this way don’t count as being on your Bard’s list for the sake of this feat… it’s a bit too powerful otherwise, IMHO.
