I've been focusing for a few weeks on balancing martial characters back into usability.. and I have just decided on a fairly harsh solution. Extra Attack is for martials. Specifically, that means that Bladesinger and Valor Bard were mistakes, and that the various other archetypes I've invented based on them are similarly unbalanced.
In Pathfinder, classes are essentially 'martial' to the degree that they have full Base Attack Bonus - Fighters got BAB +1 every level, wizards got it every other level, and the bulk of the classes fell somewhere in between. In practice, that means that if you tried to build a melee Wizard, you'd need to overcome a net minus five on attacks by level 10, and pretty damning obstacle to using casters martially.
Fifth, with its "bounded accuracy", doesn't have a truly matching mechanic, but one ability has the potential to be used that way - Extra Attack. The Extra Attack feature is essentially mandatory for a physically attacking character - dropping an attack every round is devastating to DPR, and also hurts melee versatility (shoving/grappling replace individual attacks, not the whole Attack action).
The central problem with using the mechanic in that way is that it's not sufficiently granular - you either have Extra Attack or you don't, there's no middle ground for the gish-style part-casters. A secondary problem is that the core game comes with the Valor Bard, a full caster with Extra Attack, and SCAG gave us the Bladesinger, an even more tilted caster (shield and mage armor are substantial advantages over the Valor Bard).
The solution I'm trying now: take away their Extra Attack for something more limited. Replace Extra Attack with something similar that can't stack with the other DPR increasers. A few possibilities:
I think the last one seems most promising, so I'll expand on it here.
To scale properly with the martial version, we need to match the following:
First we'll address the class abilities:
There's a scaling problem now though - Extra Attack comes online at level 5, and allows an extra die and an extra bonus damage. The cantrips come online at level 1 - at level 5, they offer an extra die and an extra bonus to the primary target, and also significant damage potential (to the secondary target, or if the primary target moves). As long as we don't allow cantrips to benefit from the weapon-focused DPR boosting feats, that's ok.. but I'd rather not have to deal with that complexity. It's almost fine without any changes - the conditional damage on BB isn't too bad, it's just that GFB damage that's consistently available.. Let's change GFB:
This makes the ability scale correctly against the primary target, but does not necessarily deal any damage to the secondary target - since it can put out the fire, it's comparable to BB in its effect on action-economy; the 1d6 damage per round wouldn't amount to much, but the additional damage from your attacks on that creature push it into the realm of mattering.
And then we can add two additional melee cantrips (alongside Booming Blade and Greenflame Blade):
These don't have the capacity for extra damage that BB and GFB come with, but they add utility and scale properly. (All of these cantrips outscale plain melee damage at level 11, but many other classes have abilities to add more damage at that level as well. Need to keep this in mind for the Magus class though - paladins have Extra Attack, and get Improved Divine Smite, but Magi will be using cantrips, and so won't need such a boost.
Changes to the Magus rogue archetype (which is going to be renamed shortly) will be pending; clearly these changes will not make sense in that context.