It'll be easier for me to list the bosses I cannot solo:
Conditions: 0 deaths throughout fight, no external buffs from other classes, may use potions
- Sofys400 - Dunkelis400 - Veltria400 - s450 - Golden s400 - Metal s400
The reason why these all fail because i probably need to get more HP, my current is 100k, these bosses all hit above that amount (or in the case of dunkelis, i didn't have the correct gear against her debuffs yet)
My recommendation for the top-fastkill-solo class will still ultimately be Alchemists due to Damage disable sets and defense-ignoring Ailment damages. It's nigh-impossible for any other class to easily catch up, even with the introduction of Lv360 skills in the far-off future.