JES II-
I think you might have got tricked into thinking Sandwich is harder, but not being a scratch golfer and obviously not having seen the conditions, I can't get inside your mind. That said, Deal is a much stouter course even now than 10 years hence. Let me summarize my views:
I think Deal is a fairer test regarding oblique and odd bounces given the terrain. Deal does not have the giant sand hills that Sandwich has which gives it more area to deflect the orb.
Deal is a more difficult course in the summer southwesterly paradoxically b/c the beat back home is very long into the wind given the out and back routing. The stretch from 12-18 offers no respite (maybe 17) especially if #16 plays as a par 4. Now, taking the routing into account, one may deem Sandwich the better test given that it exposes the protaganist to winds from all directions (akin to Shinnecock or Muirfield).
I believe Deal has a better set of greens than Sandwich. Now I have no disrespect for RSG at all--it is a regal and noble course-- I just think putting at Deal involves more contouring and artistry which lends to the difficulty.
Being an overseas member I've obviously only played about 35+ rounds at Deal but from what the locals tell me in competitions, the course plays 2 to 2.5 strokes harder than Sandwich. Our professional, Andrew Reynolds has told me the same and he should know, he tied for 22nd I believe at this years Senior Open, has been at Deal for 25+ years and was the county coach for Kent.
The hole I think you speak of is the all world par 4 6th at about 330 yards with a sand hill blocking the green. Downwind you can go for it but it can spell disaster given the precarious nature of the green.. Here are some pics Ran took: