I personally think David Silva is a better player that KDB....yes KDB can do things that David Silva cannot but Silva ran games consistently on his own...KDB only does that on occasions and is more inconsistent that David Silva was as you say....David Silva was never less than an 7/10 any time he stepped on the pitch.....KDB as you say can be awful at times and miraculous at others....
I also think David Silva affected the whole team more than KDB does - for me its a little like the argument between Messi and Ronaldo....I always preferred Messi as he was more of a team player whereas Ronaldo was all about the individual brilliance....KDB has a little of that in him (though he is much more of a team player than Ronaldo ever was) - what I mean is that KDB can come up with those moments of individual brilliance whereas everything that Silva did was for the team...He didnt get the assists that KDB did because sometimes he was making the pass before the pass that was the assist (usually the harder pass)...
I cant quantify or justify this but it always appears to me that David Silva had more football intelligence than KDB
He was also a lot more resilient on the pitch - no matter how bad things got in a match he never let his head go.....KDB does at times.
This is in no way putting KDB down - he is a miraculous footballer and a generational talent who we are lucky to have BUT for me David Silva is the best Ive ever seen in a city team and criminally underrated when it comes to talk about the best midfielders in premiership history - Id have him over Lampard, Gerrard, Scholes any day and not just cause he played for city....if it wasnt for Iniesta and Gavi along with Messi at Barca I reckon he would have played in that Barca team at some point (think Pep has said somewhere that he really wanted/liked David Silva while he was manager at Barca)