I checked, and my maxed perfect Ho Oh with Solar Beam does not make my top 6 either in DPS or TDO. Fire resists Ice, but flying gets extra damage, so Ho Oh is neutral. My level 35 Vileplumes have higher TDO!
From what I see, it sits around #13 in TDO of all attackers, (noth counting alternate movesets on the same attacker)
Edit - read the string below, very different results from pokegenie battle simulator and Pokebattler
From Pokebattler Ho-Oh sits at #2 for TDO and #4 overall