The impact of Jeff Withey on opposing defenses is in some cases easy to measure: he led the nation in block percentage last season and ranks 6th nationally this year. Why the slip to 6th? A number of factors: first, he's better offensively than anyone higher than him, and has to expend a bit more energy down there. Secondly, he plays more than anyone higher than him, and lastly is that opponents don't want to challenge him anymore.
That last point could be renamed the Withey effect over the next few years (hopefully) Joel Embiid is continuing the trend of Kansas big men who are the backbone of top defenses. Withey is the leader of the #1 two point defense in the country, allowing opponents to make just 38% of their twos. They will certainly finish in the top 5 for the 8th time in the last 9 seasons. Because of Withey, teams are taking only 26% of their field goal attempts at the rim, and are shooting just 51% at the rim, both absurdly low numbers. (for example, Elijah Johnson, who until recently couldn't buy a layup, is taking 26% of his shots at the rim and making 55% of them).
While Withey impacts strategy to an extent, it doesn't force (most) teams to take an inordinate number of threes more than they would usually take:
The above chart is what percentage of total field goal attempts are threes for each Big 12 team (in Big 12 play) followed by the same number for when they play Kansas. As you can see, while some teams take a lot more threes, some also take a lot fewer and the majority are generally close to their season averages. Some of this is because Big 12 teams take quite a few threes anyways (for a power conference at least) so mathematically it makes it tougher to see that impact. If Kansas ends up playing a team like Oregon in the tournament I think we will see a bit more impact in terms of number of attempts.
Of course, the fact that opponents generally take the same number of threes can be seen as a good thing. Opponents are most likely getting the same quality of looks from three, but they are either taking a lot more inefficient two point jumpers or they are trying to go to the rim against Jeff Withey which, as we have seen over the last two seasons, is a bad idea. Unless you're a Kansas fan.