In the first place, your comment concerning engine braking shows a complete misunderstanding of the AD system. It has no effect on any aspect of the engine's operation at all once about 600 RPM is reached.
I've had my manual decomp on my 426 for almost 2 years now and I doubt you could get your 450 started any faster than me, kicking or bump starting hot or flooded. I know my compression braking has saved me from some hairy S**t coming down the big hills at Carnegei and certainly wouldnt want to change a thing about that. The only downside to MD is on the starting line of a harescramble but so far I've gotten mine first kick everytime and have had good starts.
In the second place, my first experience with a 4-stroke with a compression release took place approximately 39 years ago, not 2. I am intimately familiar with everything that can be done with a compression release, including bump starting, flood clearing, and using it as a kill switch. In fact, I nearly didn't buy a YZ450 for the simple reason that it didn't have one. While having one would actually be very occasionally convenient, mostly while working on the bike, it is otherwise the most useless piece of crap I could imagine having on a bike with AD. You simply won't ever miss it.
And from extensive experience with bump starting a long list of thumpers you've never heard of with a compression release, including a YZ426, I promise you that there's no way it's easier that way than with the 450 AD cam. Trust me.