I wouldn't say SYT is slow. He was just touched off by Rewilding at last year's Royal Ascot in the fastest run race of the day, having gone 2l clear 2f out. In the Eclipse he beat Workforce in another fast run race (exc the 2m marathon, was the fastest of the day again). You can't call a horse slow if he clocks fast times.
Looking at his Melbourne Cup run on soft
"Always going well in 6th or 7th, closed up 4f out, 5th and closing on outside 2 1/2f out, led over 1 1/2f out, soon ridden and ran on, headed approaching final 110yds, unable to quicken, lost 2nd final 50yds"
This shows that he clearly goes well on soft.
His run at Royal Ascot last year shows he likes the course but couldn't quite hang on over the 10f on fast going.
If he can lay up with top horses in fast run races on fast ground and is also comfortable on soft then, as long as it stays soft for Ascot, I would be very tempted to take on the mighty Frankel. What is there to lose?