I think its more than fair to judge a DOF as you would any other entity of the club be it the manager, players or owner/chairman.
He's been here 2 years and whilst his signings have in the main been better than Walsh's those all mainly came in the first summer window.
His second window was really poor - Kean may well develop into a top player but right now he offers little, Iwobi is rubbish and screamed a panic buy, Delph is a bad egg and bang average, Lossl - the German Ghost. Only Gbamin can realistically be hailed as a success and thats totally dependent on him actually getting on the pitch and adjusting to the league which we dont know how well he will do. Add in the lack of options at CB, RW & up top he hasn't done as great a job as some make out.
His lack of use of the January window especially this one when we are in a battle for Europe is also frustrating.
Basically he's had 1 good summer window, 1 bad & 2 non existent January ones. He simply has to get the summer one right otherwise people wont be questioning the manager like they did with Silva they'll be questioning this bloke.