737 incognito
I can see your point a good defensive approach to flying.
I think the requirement for 2 dest alts is designed to cater for a single event at either of them occuring before you make the decision to divert. Once you make the d to divert then I guess statistacaly you are in the same regime as any other diversion.
As an aside if the weather was that poor at Dest I'd carry 1/2 hr of holding fuel ontop of the div requirements, weight permitting to give me thinking time and to give the wx a chance to improve or fuel for a second approach although there is no legal requirement to do so.