If things keep going like this, we could need a PS4 v.s. PSP chart, not just 3DS v.s. PSP. Heck, PS4 did less than what PSP sold back in 2006, not even considering 2008 (legitimately a good year for the platform). Next month should represent an exception, though, Batman is coming.
And again, we need the most updated Wii U only All-Time US Chart to be posted to understand if Splatoon really sold that well on eShop. We just have that it was higher than all Humble Bundle games on June 3rd already...which could actually be an indication of sorts. You see, current eShop charts count the sales for each title for the latest two weeks. So, for example, if Splatoon was the best selling title on the eShop on June 3rd, it doesn't mean it's just selling better than what the other titles are doing now, but that its sales are better than what those titles sold between May 20th and June 3rd, so that would take account of all Humble Bundle sales (or at least, all the codes being used) up to June 3rd. Still, we definitely need to see the All-Time Charts to get a confirmation on this matter.