They're not. Neither one is perfect by any means, but design wise the Icom is several years newer, and can be easily remoted for mobile use. It also has marginally higher power on the VHF/UHF bands.
I've not owned an 897, but I have owned a 857, and even the 706MkIIg is a better radio overall. My biggest complaint is the little screen, and funny programming.
Or, you could buy separate radios. If you want a lot of power, and you have the room for the remoted head, the Kenwood TS-480 Hx is a decent radio. No VHF however. At 200 watts, it's a poor man's amplifier.
Lastly, I wouldn't consider a Yaesu 450 for a mobile unit.