Looking at this piece by piece,
Quoting: jjkhairaELTE99
you are trading rfa rights of a bottom 6 player for a hometown kid that is still young
Because of the Kraken's forward depth, both Sprong and Yamamoto would likely be bottom six players in Seattle. Sprong has flat out performed better than Yamamoto this season in a lesser role. The difference between them in age is also only a year, so both could still be considered young players.
Quoting: jjkhairaELTE99
with a friendly QO that you still control for a few yrs
Both Sprong and Yamamoto still have RFA control, and Sprong's QO is only $900k this offseason, while Yamamoto's will be $3.2M.
Quoting: jjkhairaELTE99
that brings physicality and forechecking to the lineup
Yamamoto is the better defensive player for sure, but Sprong has improved his game to become much more of a two-way player. I would say that the gap between Sprong's offensive output and Yamamoto's is greater than the difference in their defense.
That's all not to say that there's zero chance the Kraken wouldn't entertain a trade of this basic framework, but if they did, it wouldn't be for the reasons listed here. I could envision a scenario where GMRF decides to sell high on Sprong and buy low on Yamamoto, but in that scenario the Kraken would want a draft pick coming back to them, not going out.