Some of the combinations seem to get more out of being paired. For example a wizard/fighter gets fighter hps & HD, full armor & weapon proficiencies, can have CON saves which are a big boost, and full casting including spells like Shiedl which synergize well with heavy armor. Oh, and more ASIs, which could be used to boost wizard ability scores or take feats that benefit the wizard side.
But he will have the same AC and fewer spell slots than a Fighter 1/Wizard X using melee cantrips to do his fighting. And if he's spending his ASIs to boost wizard ability scores, he's not boosting his fighter scores, so his fighter levels wind up being mostly irrelevant.
Say I go to BrockJones.com and roll up
12 14 17 11 15 6
(Those are pretty nice rolls BTW and I'm not sure how that will affect the below analysis.) Let's say that's a human Heavy Armor Master with Str (15) 16 Dex 12 Con 14 Int (17) 18 Wis 11 Cha 6, and I'm trying to decide whether to concurrently multi-class or use a PHB buffet-style multiclass.
At 100,000 XP (nice round number), I would be either:
Fighter 1/Abjuror 11, Str 16 Dex 12 Con 14 Int 20 Wis 11 Cha 6 HP 78 with one feat/ASI left over and slots 4/3/3/3/2/1 (73 spell points), relying on melee cantrips like Booming Blade for 3d8+3 (16.5) damage plus 13.5 as a rider.
OR
9th level BattlemasterAbjuror, Str 16 Dex 12 Con 14 Int 20 Wis 11 Cha 6 HP 76 with two feats/ASIs left over, superiority dice every short rest, and slots 4/3/3/3/1 (57 spell points), relying on melee attacks for 2x d8+3 (15) or melee cantrips like Booming Blade for 2d8+3 (12) plus 9 as a rider.
Neither one is inferior to the other, and it's not obvious which one I should pick--but if I don't like planning "builds" in detail, the Battlemaster/Abjuror is less finicky and, depending on what you think a class is, perhaps more aesthetic. (Hence this thread. I wouldn't have bothered writing something up if there weren't at least
aesthetic advantages to old-school multiclassing.)
On the other hand, a paladin/ranger doesn't get a great deal. HPs are about the same, proficiencies are about the same, both get extra attack, etc. They do have two different casting progressions but both at half speed,and the speed is delayed due to the XP split.
Hmmm. Compare a 12th level Paladin to a 9th level Paladin/Ranger (assuming the DM offers Paladin/Ranger as a valid multiclass combination). 4/3/3 slots on the single-classed guy vs. 4/3/2 and 4/3/2 on the multiclassed guy. 3 ASIs for the single-classed guy, vs. 2 ASIs for the multi-classed guy, and the single-classed guy has Improved Divine Smite for +d8 radiant damage on melee hits while the multiclassed guy has +d8 via Colossus Slayer or a third attack via Break the Horde, plus random stuff like advantage on saves vs. being frightened and ability to ignore nonmagical difficult terrain. The single-classed guy has significantly more HP (about 30% more depending on Con).
It's not at all obvious to me which one to take, so you might as well just take the one that fits your character concept better.
This isn't bad - not all combinations are created even. But it seems to push for characters to take two very different classes and leaving similar classes. Like everyone will be a "full caster/martial type".
Am I needlessly worrying?
If warrior/warrior multiclassing like Champion/Barbarian turned out to be a thing under old-school multiclassing, I would be interested and pleasantly surprised, but encouraging it isn't a design goal. The classical multiclass combinations are fighter/mage, fighter/thief, fighter/cleric, mage/thief, fighter/mage/cleric, fighter/mage/thief, and maybe a couple of others I'm overlooking--those are the ones that
have to work for me to consider multiclassing rules a success.
But I think combinations like Paladin/Barbarian (if allowed by the DM) would be perfectly viable and quite interesting, while also not crowding out regular single-classed Paladins or PHB-multiclassed Paladin/Sorcerers. There are pros and cons to each of them. The only combination that my powergamer instincts tell me
not to pick is the single-classed Paladin; it's always better to PHB-multiclass away at some point (e.g. Warlock 2 dip, and probably some Sorcerer levels) instead of sticking around for the lame Paladin capstones. But a Paladin/Barbarian doesn't have that option--he's a Paladin/Barbarian for life, and as a designer I like that tradeoff.