Control Valves for Fuel Oil Heat Exchangers

Design project where we want to use fuel oil to fire a boiler. To do this we have to heat the fuel oil first so it is being sent through a Fuel to steam heat exchanger. The manufacturer is saying that it is better to control the heating using a two position control valve. We want to use a modulating control valve to control better. Vendor explains the modulating steam control valve in this application does not address the reaction and full range necessary for accurate control. Why not use a 2/3 1/3 valve arrangement? Anyone have any pros and cons on this?

Thanks.