Assuming that lost sales need to go somewhere is a mistake. When the console market crashed in the 80's there was a point where Nintendo hadn't yet entered the game, and sales of consoles were just awful. People didn't move from buying Atari's to buying some other gaming device. They just literally stopped buying consoles. Both the 3DS and Vita were extremely underwhelming compared to their predecessors. When all options on the market are bad, the market will shrink. Smartphone games shaved about 20 million off the top of 3DS lifetime sales. But Nintendo's price/drought/naming/eyestrain shaved more off lifetime sales. A properly launched and priced 2DS XL in 2011 would have done 90-100 million units easily.
You are making the same mistake as above. Nothing needs to grab buyers. What grabbed Atari buyers when the console market crashed in the 80's? It wasn't Nintendo. They didn't show up until after the crash. You can't explain Atari sales losses, by saying that they all went to Nintendo. What best explains it is that Atari and all other consoles sucked at that point in time. So people flat out stopped buying them.
Mixing a new market full of mistakes crashing to a contraction (will you try and claim there was some crash and that if Nintendo decided for a new HH instead of Switch it would see 100+M confortably? No, because it is very clear the market shrunk due to indirect competition by substitive).
New HH instead of Switch? Switch Lite hits the $205 or less sweet spot of pricing, that the Nintendo Handheld market has always thrived on. Track sales of Switch Lite over the next few years, account for the fact that regular Switch exists, and you're essentially tracking the HH market today. If Switch Lite does less than 50 million, then we know the market did indeed shrink due to Smartphone games. If Switch Lite does 50 million or more, then clearly, had Nintendo launched just Switch Lite in 2017 and no dock it would have sold 100+ million.