Yes most 2 guard are scorers on defense but also should be one your best defenders too.
That triggered me into wanting to take a look at the relative defensive prowess of starting 2 guards for teams that will likely make the playoffs this year. A few caveats: in the East I went with Boston, New Jersey, Philly, Indiana, Toronto, Milwaukee, Atlanta, and Miami. In the West, I went with LAL, LAC, Blazers, Nuggets, Jazz, Warriors, Mavericks, and Suns. There are undoubtedly a few other teams that could make the playoffs, but this list is good enough for these purposes. As a measure of defense, I used career DRtg. As far as position and player selected, I used ESPN's depth chart designation for starting 2G. With that, here's the list, broken into The Good (100-105 DRtg), The Bad (106-110 DRtg) [okay, average, not bad but Clint Eastwood says work with me here], and The Ugly (111 plus):
The Good (100-105 DRtg)
Bucks - Donte DiVincenzo - 102
LAC - Paul George - 102 (Note: tailed off to 106 the past few seasons).
76ers - Danny Green - 103
Nets - Caris LeVert - 104
The Bad (106- 110 DRtg)
Celtics - Marcus Smart - 106
Pacers - Victor Oladipo - 106
Raptors - Fred VanVleet - 107
Jazz - Donovan Mitchell - 108
Lakers - Dennis Schroeder - 109
The Ugly ( 111 plus DRtg)
Nuggets - Gary Harris - 112
Blazers - CJ McCollum - 112
Mavericks - Tim Hardaway Jr - 113
Heat - Duncan Robinson - 113
Warriors - Andrew Wiggins - 113
Suns - Devin Booker - 115
Hawks - Kevin Huerter - 116
So, by my probably poor analysis of prospective playoff teams, only about four starting 2Gs are good on defense, another 5 are average, and 7 (including CJ) suck.