First off, the final-blow system does not differentiate between mains and alts. the 1 in 21 logic ratio still answers his initial question about "rate".
Now regarding the sharing:
Riverbummer's "guildies" (disputatively alts but we'll suppose they are real for the sake of argument) are also struggling for that (near-100% damage) that Riverbummer is taking for him/herself. This pot contains 10k reputation, and much coins/credits depending on the size of the boss, and if this realm is not new, it will provide much more than the 10million coins in the final blow stage.
There are reasons why I stop at 40% on my realm, for my guildies, even though I could easily do over 80%.
Remember: when you assume, you make an "ass" out of "u" & "me"





