Eyeballing the four year guys since 2015, and it looks to me like they out-perform their average draft slots. This is quick and very dirty, so I've probably missed some guys, but this is a list of four year college players drafted outside of the lottery (I've included guys like Semi who transferred and sat out a year- ymmv with whether it’s wise to include them), followed by their draft slot and year, total minutes played, then Win Shares/48:
2019
Matisse Thybulle - 20th; 1315; .084
Brandon Clarke - 21st; 1375; .174
Dylan Windler - 26th; N/A
Cody Martin- 36th; 958; .058
Justin James- 40th; 235; .030
Eric Paschall- 41st; 1733; .063
Admiral Schofield- 42nd; 368; .017
Terrance Mann- 48th; 416; .078
Quinndary Weatherspoon- 49th; N/A
Jarrell Brantley- 50th; N/A
Justin Wright-Foreman- 53rd, N/A
Marial Shayok- 54th; N/A
2018
Grayson Allen- 21st; 1214; .051
Chandler Hutchinson- 22nd; 1474; .038
Jevon Carter- 32nd; 1572; .050
Devonte Graham- 34th; 2993; .063
Svi Mykhailiuk- 47th; 1771; .038
Keita Bates-Diop- 48th; 1247; .059
Vince Edwards- 52nd; N/A
Devon Hall- 53rd; N/A
Kevin Hervey- 57th; N/A
Thomas Welsh- 58th; N/A
George King- 59th; N/A
2017
Derrick White- 29th, 3544; .112
Davon Reed- 32nd; 289; -.039
Josh Hart- 30th; 5041; .085
Wes Iwundu- 33rd; 3220; .063
Frank Mason- 34th; 1537; .038
Semi Ojeleye- 37th; 2801; 065
Damyean Dotson- 44th; 3370; .044
Sterling Brown- 46th; 2628; .074
Sindarius Thornwell- 48th; 1511; .035
Monte Morris- 51st; 3738; .135
Alec Peters- 54th; 225; .055
Jabari Bird- 56th; 115; .098 **** Career cut short by domestic abuse charges
Jaron Blossomgame- 59th; N/A
2016
Caris Levert- 20th, 5601; .065
Brice Johnson- 25th; 107; .062
Malcolm Brogdon- 36th; 7051; .121
AJ Hammonds- 46th; N/A
Jake Layman- 47th; 2299; .064
Michael Gbinije- 49th; N/A
Georges Niang- 50th; 1585; .082
Joel Bolomby- 52nd; N/A
Marcus Paige- 55th; N/A
Abdel Nader- 58th; 2083; .048
Isaiah Cousins- 59th; N/A
Tyrone Wallace- 60th; 1639; .006
2015
Jerian Grant- 19th; 4998; .080
Larry Nance Jr.- 27th; 7532; .133
Anthony Brown- 34th; 762; -.016
Rakeem Chrismas-36th; 225; .105
Darrun Hilliard- 38th; 859; .016
Josh Richardson- 40th; 9732; .090
Pat Connaughton- 41st; 4521; .109
Joe Young- 43rd; 1077; .016
Marcus Thornton- 45th; N/A
Norman Powell- 46th; 5819; .098
Aaron White- 49th; N/A
Sir'Dominic Pointer- 53rd; N/A
Cady Lalanne- 55th; N/A
Branden Dawson- 56th; N/A
There's probably a bunch of UDFA guys that would be interesting to look at, but the only ones who come to my mind immediately as recent four year guys are FVV, Terrance Davis, Caleb Martin and Tacko. Looking at 2014 without going through the whole draft, and Napier, Joe Harris, Dwight Powell and Jordan Clarkson all fit the bill, if memory serves
Anyway, this is more of a book mark for when I have time to look deeper as to how the four year guys compare in terms of draft value, but the guys in bold have, to my mind, unquestionably outperformed their draft slots. The guys in italics have either underperformed or played less than 200 minutes total in their careers. The rest are either pushes or TBDs.
Overall it does seem like there's a lot of good value there. A lot of the guys who didn't do anything were drafted really late, between 45-60, and those guys generally don't do much anyway. This deserves a more thorough look, but I figure some might find the list interesting in and of itself.