I think this is all pretty silly - and especially in relation to last night. Geno against Colgate did not want to embarrass his gracious hosts, on what was really more of a celebration party at which a basketball game broke out, than a competitive game. He started the game playing a half court non-aggressive zone defense as opposed to a full court pressure defense. That allowed Colgate to get a little confidence and stay in the game early. It wasn't until about half way through the half that he had the team play a more aggressive style of man defense.
As for the rest of it - Uconn is still finding their legs in terms of 3 point shooting. And they are facing teams desperate enough to shoot a lot of threes from beyond NBA range who for the past week have been hitting them at a rate that cannot be sustained. Will the defense on the arc tighten up as the season progresses - yes. Will Uconn guard players tightly 25 feet from the basket, probably not. Will the torrid streak from opponents continue - no.
And as for looking at three point percentage defense in comparison to other teams - lets wait for a little larger sample size, and even then, the best defenses will typically be the team that plays the worst offensive teams. Look at top defensive stats for any full year and they are filled with pretty terrible teams who have played even worse competition, with a few top teams scattered in.
At this point in the season, Uconn has played three of the top 12 offenses in the country (ND #5, DePaul #10, Ohio St #12), throw in Nebraska at #23 and that is a 'murders' row' of offenses. And just in anticipation of Friday and another moan, FSU is #10 in field goal percentage though their offense is a not shabby #34.