OP's math is slightly off. The poison damage inflicted in turn 1 is not taken until turn 2, that added in 2 not taken till 3, etc. This adds up considerably. (or rather, subtracts from the total)
With that in mind, let's compare turn by turn, the total damages of Titan and Arsenic(unupped):
7 14 21 28 35 42 49 56 63 70 77 84 -Titan
2 5 9 14 20 27 35 43 53 64 76 89 -Arsenic
That's 12 turns for Arsenic to overtake Titan, and Titan can't be blocked. Upped takes 11 turns, both hit the 100 mark in 12.