In terms of offers we've seen around here, this is fairly weak. The 1st + 2nd/prospect might be competitive with other offers, but not if you're also expecting the Ducks to eat over 12M in unwanted salary between Byron and retention.
Paying Byron more than Rakell next year and being stuck with him an extra year is highly undesirable for Anaheim. You're offer doesn't reflect that at all.
Rakell is likely worth about a 1st + 2nd/prospect (or more) on his own. If you expect 50% retention and want to tack on a bad contract that runs longer than Rakell's, you definitely need to add significant value. Whatever Rakell is deemed to be worth, the financial considerations you are requesting would require an additional 1st round pick or something in that neighborhood. You're asking the Ducks to eat waaaaay more money than they would be willing to unless highly incentivized.