Compared with most other cars of the same age I'd say they were very strong, that's why there's so many of em left!!!
I've carried out quite a bit of private crash testing on mk2 golfs over the years

First test involved writing off a mk2 astra, golf lived to tell the tale.
Second test involved removing several roadsigns as I gleefully hurtled my way straight over the middle of a roundabout (in the same golf as test one). I didn't bother to fix it this time but sold it on for spares. About 5 years later I saw it driving through newmarket still soldiering on!!!
Third test involved careering out of control at 70+mph straight into a steep bank on a country road in my last oakie. It ended up wedged between the banks on either side of the road, once I 'd managed to kick the door open I emerged with just a broken nose from head butting my momo. The car was dead but I'd survived

Now I'm happy with the strength of the mk2 I don't feel the need to crash my current one!!!