There has definitely been a ratings 'creep' over the last few years and I don't think that it's fair for a horse to have the same rating for both park and National/Cross Country fences.
This season's ratings started to go wrong with the over-rated King George and, because of that, they've had to go high with Cheltenham and Aintree. Do I think Al Boum Photo and Kemboy can run to 175/174? Yes. Do I think they did at Cheltenham and Aintree? No.
In today's money, Tiger Roll could be 170 over National fences but I doubt he'd be worth more than 165 in a normal chase. However, we'll probably never know because he hasn't jumped a park fence in public for nearly 18 months. For comparison, Cadmium came 4th in a handicap in February off 147 yet he won the Topham easily off 152 and is now upped to 162. I'm prepared to concede that the nature of the track helped him but he took to the fences so well that his new mark is just not representative of his recent form.