This is factually incorrect. You simply cannot compare level x to level x in 2e because there were too many class specific variances. Bards advanced fast yes but they had a completely different spell slot progression that capped at 6th level spells. They capped out at 6th level spells & didn't even get one till level 16.2E - Advanced extremely fast, to the point where you actually got fifth-level spells before a Fighter/Mage did. Were more than a "half-caster". A 2/3rds or 3/4s caster, which is more appropriate. Was a true Jack of all Trades.
I'm not going through the level to spell slot ratio for every level but here are a few unless I screwed up copying or typo'd
- Bard5: 10,000xp 3 1st level slots 1 2nd level slot
- Bard 10: 160,000xp 3 1st level slots/3 2nd level slots/2 3rd level slots/1 4th level slot
- Bard 15: 1,100,000xp 3 1st level slots/3 2nd level slots/2 3rd level slots/2 4th level slot
- Bard20: 2,200,000xp 4 1st level slots/4 2nd level slots/4 3rd level slots/4 4th level slot/4 5th level slots/3 6th level slots
- Wizard5: 20,000xp 4 1st level slots 2 2nd level slot/1 3rd level slot
- Wizard 10: 250,000xp 4 1st level slots/4 2nd level slots/3 3rd level slots/2 4th level slot/2 5th level slots
- Wizard 15: 1,875,000xp 5 1st level slots/5 2nd level slots/5 3rd level slots/5 4th level slot/5 5th level slots/2 6th level slots/1 7th level slot
- Wizard 20: 3,750,000xp 5 1st level slots/5 2nd level slots/5 3rd level slots/5 4th level slot/5 5th level slots/4 6th level slots/3 7th level slot/3 8th level slots/2 9th level slots
- Priest 5: 13,000xp 3 1st level slots 3 2nd level slot/1 3rd level slot
- Priest 10: 450,000xp 4 1st level slots/4 2nd level slots/3 3rd level slots/3 4th level slot/2 5th level slots
- Priest 15: 1,575,000xp 6 1st level slots/6 2nd level slots/6 3rd level slots/6 4th level slot/4 5th level slots/2 6th level slots/1 7th level slot
- Priest 20: 2,700,000xp 9 1st level slots/9 2nd level slots/9 3rd level slots/8 4th level slot/7 5th level slots/5 6th level slots/2 7th level slot
Bard got their first 5th level spell at 13 (660,000xp) compared to wizard & priest's 9(135,000 xpwizard/225,000xp priest). Yes it's popular to point out that thief table PCs (like rogue) got experience for gold on dmg70 but you can't ignore that wizard & priest table ones got it for casting spells making scrolls or potions & crafting permanent magic items on the same page.