Didn't say it will sell closer to 2M gap than to 5M, I said that is less likely that the gap will be 5M than 2M. Probably something like 3-4 is more likely.
The beggining of this year had better games legs from holiday and PS4 at a little weaker position than last year, that helps out a lot the up average of Switch. But to have 30% increase on holidays will be a lot harder.
To reach those 3-4M then Switch may not outsell the PS4 by more than 1-2M through October, and sell on par in November, as the 2M gap in December will certainly happen again.
I seriously doubt that to be the case, even with a pricecut for the PS4 and no pricecut or revision for the Switch.
Switch is selling without any releases on par with the PS4 with big releases (like, The Division 2 this week for instance). This can go on until Super Mario Maker 2, where Nintendo starts shifting into higher gear this year. Come summer, and the slew of Switch releases and nothing big on PS4 side will make the gap grow pretty fast during summer and fall, before the PS4 getting trashed by the Switch during the holidays.
The Nintendo eShop rating Thread: http://gamrconnect.vgchartz.com/thread.php?id=237454