Something of a circular argument. A bit like when in Gavin and Stacey, that Gavin’s mum was thwarted from joining a protest about a new mobile phone mast because she didn’t have any signal.
Indeed, also local infrastructure is needed for locals to get things that they need, so there's lorries already using those roads and whist the extra traffic might mean a slightly reduced time between resurfacing, maybe up to 2 years sooner (assuming surface dressing is done every 7 years and full resurfacing every 14 years, that's still not a big deal).
Up to 600 movements a day is, unfortunately, a common line in assessments. The reason being that this is the cut off point for severity for HGV moments. As such anything which can claim that is well below value will generally stress test to that value as a worst case (even when measures, such as swapping movements to rail, have been introduced) as it simplifies the process.
For example, a site is having 50 HGV moments, it's tested to "up to 600 HGV movements" and is acceptable. During the process, it's found that due a 3 week period HGV moments will triple (so 150) without this stress test the application would need to redo that assessment. The Locals would feel aggrieved and that "this was what they wanted all along" and other such reasonable comments (and maybe a few less reasonable ones).
By having the stress test, whist the locals may still feel betrayed (the actual number has increased significantly), there's no need to revisitthe assessment.
As whilst the expected number has changed, the assessment number hasn't.
200 HGV movements a day along a road isn't all that high.
In the peak hour that's one every 6 minutes heading one way and in the same 6 minutes one going the other (assuming an even flow by direction).
I had a boss who when confronted by objections over something like this (I think that it was talk of "that means this road will have a car every 60 seconds") stood in the appeal room and said "OK, let's see what that's like" and looking down to his watch said "car" and then waited and carried on looking at his watch, waited for the full minute to pass and then said "car".
There's a good reason health care staff rarely take your pulse due the full 60 seconds, as when you aren't doing a lot it feels quite long.
One final point, where residential road have food waste they will routinely see "up to 4 HGV movements a day" (one entering for general or recycling, one entering for food waste and then the corresponding 2 movements for the lorries leaving).
As such up to 20 is up to 5 times that number, noticeable, yes, disruptive hardly.