No. Defense rating does effect recruitment because it effects settlement happiness and that effects recruitment. Productive, happy settlements recruit settlers faster (or more effectively, however, you want to look at it) than unhappy, unproductive settlements. Having a very high defense is paramount for high (maintained level) of happiness. As @arras noted, defense effects attack frequency, and this effects happiness, thus effecting recruitment. These things are interconnected, not distinct.
Also, the first time you turn on a recruitment beacon, you'll immediately recruit 1-2 settlers in that settlement.
Clarification: CHA + 10 is not some guess or anything like that. It is stated in the official guidebook.
Note: PS4 version has a serious glitch/bug that allows continual recruitment of settlers. This goes along with the glitches/bugs on that version such as the shipment duplication cheat. The continual recruitment of settlers past CHA +10 (plus any gear boosting, of course) does NOT happen on PC, nor is it possible to do the shipment duplication glitch/cheat on PC, at least not for my extensive testing.
I have not seen an Xbox One player demonstrate such glitches, nor have I been able to duplicate them on PC or seen a PC player demonstrate them.