It’s all about creating systems that utilise each players capabilities.
Last season Silva developed a robust and effective defence in which Gana was integral (as well as Zouma). But it took 3/4 of season to evolve.
My concern is replacing Gana with Delph means altering the system and possible having to face a disrupted start to the season.
Like for like would have been my preference.
Think Delph has been brought in to to enable a 4-3-3 at times myself, there were games last season were we were just put muscled and battled in midfield and we clearly needed another body in there, Delph in the mobile 8 in my opinion, gives us a different dimension and option, would expect a different Idrissa replacement as an anchor.