Shift grabbing would only be OP with this change if the counselors were too close to jason when he begins to shift and if they weren't prior to the beginning of the shift. It wouldn't change the interaction of Stalk+Shift as counselors wouldn't know the shift was coming if jason was in stalk so the grab would already be easy.
In a way it will encourage counselors to not wait around close to jason and punish group ups if one person tries to split away from the group to do objectives, further punishing the bully group playstyle.
For characters with less stamina that would need to stop to regain stamina, this would force them to play around the cabins a lot more instead of wandering around in the middle of the forest (the only iffy place would be at the repair shop area of Crystal Lake).
For faster characters, it would hopefully reduce their effectiveness at evading swings/grabs when literally touching jason and make attacking jason with a weapon a lot more risky. A benefit of this could be the fact that they may begin to focus more on transporting items around the map for slower characters, which is a much more beneficial use of these characters.
In regards to the concerns around jason being stunned all the time, a good first change could be to just reduce the availability of consistent one hit stun weapons such as baseball bats and flare guns as one of those 2 seems to spawn in every cabin right now.
The decreased spawn rates of these items could be coupled with an increased spawn rate of weapons such as pots and pans as they are okay for stunning but not always a guarantee, while also being something you'd expect to find everywhere in camping areas. This would mean that there would still be the same general volume of weapons on the map each match, but good weapons would become more of a luxury for counselors similarly to how they changed pocket knives.
For characters that basically rely on being able to stun jason as they have high strength (mainly Bugzy players), they could tweak the higher value strength stats to allow these characters to stun jason slightly more consistently than other characters so they can still help protect slower counselors.
TLDR: There is a VERY low chance of shift grabbing becoming OP from this change (in my opinion) and it would cause counselors to actually be SCARED of jason again as they wouldn't have as much power as the previously had.