Riiiiiiiiiight!
So if these "O2 Gurus" and the "HTC Engineer" told you to jump off a bridge into the moon made of cream cheese, you'd be all over that too? Clearly everything that the companies trying to fob you off are saying is true...
There are ICS ROMs for the Sensation and the S2 that have been running fine for 6 months at least. I used to work with a lad who had ICS on his S2 in September last year, it was seeing that that made me look to put it on my HD2. ICS isnt the issue, the OS is sound, otherwise phones like the S3 and the HTC one X wouldnt be able to run it without issues, which they do.
Click me to see the Sensational light!
Click me to go to S2 world and see ICS ROMs that work
Maybe your Gurus and the engineer need to learn that Android is open source for a reason...