I think there is a tad more to it than thrust always drops off from the static case as aircraft speed builds up.
The intake has a part to play in obtaining the eventual compressed air that the engine uses to keep itself pumped up (using the everlasting balloon analogy) While the increase in efficiency of overall compression due to the intake as speed initially builds may not be huge, the compressor can still do better when it does not have to suck all the air in. A bit of ram is helpful.
Once the speed builds the increasing drag effects will quite soon overwhelm the benefits of feeding the compressor better. Once you are supersonic though its all change and the intake provides perhaps 40% of the necessary compression – check with WOK if you doubt that.