I can give you two "make it make sense" things:

#1: Have you looked deeper into who else Reggie had next to him? Those Philly lines would have wreaked havoc on Packer OLs of those days even WITHOUT Reggie White. You couldn't really game plan to just take away Reggie - the others would kill you. Vs. in Dallas, they haven't had a 'rest of the pass rush' anywhere near that level. So it is MUCH easier to 'game plan' to take away one guy (i.e., Parsons).

#2: Have you looked at the overall quality of the OL in the late 80's/early 90's when Reggie was wreaking havoc on the GB OL? Compared to what they've had the last couple of years vs. Parsons, there's no comparison. Even WITH the injuries (and some guys playing who maybe shouldn't have been), they've always been able to cobble together a top-10 in football type of performance in pass protection lately. Compare that to the late 80's/early 90's, when Don Majkowski was running for his life. Two of those years (1990-91) featured Tony Mandarich starting at OT - and Reggie absolutely ate him alive. But it's really a testament to the OL coaching, almost more so than the talent they've had lately.