I looked at several of the USTA sections to see what a #16 ranked player would be nationally.
SoCal … 135
Intermountain … 324
Missouri Valley … 336
Pacific Northwest … 526
Eastern … 146
Florida … 129
The range between sections does seem extreme. With that being said, I looked up the players on tennisrecruiting and players around #500 nationally were all 3 star seniors. My son is a 3 star 8th grader and he beats mostl of the 4.5 players in my district. He would not be a ringer on the 4.5 team, but he would definitely be in the top half of the group.
A 3 star senior is not a 4.5. Not even close. 5.5 is difficult to quantify. The range of talent in that group is large. You are either a 5.0 or 5.5, hard to tell.