I disagree, unless you care about assassinate which is extremely useless in end game content w/o insane investment just due to gear limitations, if you really want to insta kill melee play a monk, 20 assassin over a 2 monk splash is worse imo.
20 rogue over 18 nets you 1d6 SA and a rogue feat, which at that point is going to be something like crippling strikes or skill mastery pretty meh
the 2 monk splash gets you 2 extra feats (but you have to spend 3 feats to get the monk stances so a wash more or less) but w/ that its 12% DS +4 dex and 1.5w from dance with flowers twist and the option for more survivable stances if you care
Vistani capstone is 20 mp 5% attack +2 all stats, Assassin is 10 mp 4d6 SA and +dex and int, the extra 10 mp and attack speed handily beat the 4d6 SA
Assassin and Vistani t5's are both kinda **** tbh both don't give you anything to huge besides again assassinate which isn't great in high skulls, if anything Vistani is better from a pure DPS standpoint due to the +10, +3 to hit and damage, and the 25% uptime +1 crit and threat
If you really want SA, you could even go 18 1 monk 1 ranger and put 1 point if you have the universal tome into DWS for the 1 sneak attack so split would be 41 vis, 31 assas, 8 harper, 1 DWS
I don't see how in any situation if you're pushing for pure DPS pure rogue is stronger than a splash.
Quick edit: from this guy:
https://www.ddo.com/forums/showthrea...f-you-beat-me: hes running a 111 assasinate dc which just isn't good enough for high skulls sharn content, my monk had a dire charge dc of 118 and it still failed a good amount, assassinate is a tough sell in the current game state w/ it not taking combat mastery bonuses