Bonnie Rose Doesn't have Merchant, she has to rely on two other troops with Merchant to achieve the results you mentioned (+25% each). In addition, she only gains 15 gold per cast (so 23 including the Merchants), it will take her 7 casts to get to the max. After all of that, she will only do a max of 96 damage (assuming all guild/kingdom level bonuses).
Compare that to a traited Pharos, he can reach 100 souls alone (without any extra Necromancy troop), his max damage in that case would be 119 (assuming bonuses as above). If you add 2 more Necromancy troops (at +50% each), his max damage would be 159. Or, you can use two of him, for a max of 179 damage. And the best part - he can achieve that in 2 casts, and often enough he fills himself, so there's a potential for 2 casts in a row, the second already doing impressive damage (69-99, depending on the cases above).