I agree completely. The hardware of Amiga in general is more than capable to run decent software for displaying graphics and texts simultaneously. Heck, that's what the whole bloody machine was famous for! Especially the more expanded Amigas (I am again referring to my own Miggies) can be easily compared to perform like a fast 486 or an early P1.
I think you're nmissing something very fundamental. The CPU has to decode the graphics first, before they can be displayed. Jpgs especially, take a lOT of processor time and that's where the slowdown is. It's nothing to do with the actual displaying, it's the preparing of the data to display. And even thougb I have an 060 with 196mb RAM, displaying jpgs using WarpDT is still considerably slower than on a PC.
Having said that, as I said earlier on, my Amiga is easily as fast as my 1.5mhz laptop, on non-graphics pages, if not faster. So I would suggest that IB is very well written, but with a slow CPU, no amount of brillant coding will increase the Amiga's speed.