It's a bit of both, if Switch were just a handheld it would have likely done 3DS numbers
I actually disagree if the switch released Just handheld I believe it would have easily surpassed 3DS numbers please remember that system moved over 70 million units despite not even having every single last major Nintendo property so if the switch released and it was let's say only a hand held with no way to HDMI out if you consider nintendo's no longer making home consoles it means every last game they made would have been on that platform which means it would have moved over a 100 million because literally this is not the fucking first time they had a handheld move 100 million so why would it suddenly just move 70?
So I don't believe the 14 or so million who owned a wii u would just magically stop playing Nintendo systems just because.
I believe the primary reason behind its success is its portability because that was already the biggest factor between wii U and 3DS even with them sharing the same games the 3Ds still sold more units
Super smash brothers on 3Ds literally sold more units
We even have examples of Mario kart doing that
Shit we have examples of Mario kart literally moving less unit on the wii u and then succeeding on the switch to literally proved that that portability was the factor behind it success because if it was just solely the games themselves why the fuck didn't those people buy a wii u? More people bought Mario kart than literally purchased a wii u lol
So from 8 million to 60 million, clearly Mario Kart 8 had nothing wrong with it, merely that it was on a home console. Majority of Nintendo's hardcore base is on portable...
Even with BotW, let me remind folks FOR YEARS that was only known to be a Wii U game in development, yet that wasn't enough to get folks buying a Wii U in massive numbers in hopes of playing it, yet broke records on Switch. So I don't really buy that much that BoTW would have been any different then what we saw with Mario Kart 8 on Wii U, BEST SELLING on Wii U....yet low selling in general compared it its portable counter part.
I think we have more then enough to show that if just released with zero HDMI, it was very likely moving well beyond 3DS, if 3DS can move 75 million, Switch in this theory with all hands on deck is moving 100 mill like their past handhelds easily.
I think we have more then enough to show that its successes is deeply rooted in it being portable when the very same games moves 8 times as many units despite it existing for years else where, clearly the "games" wasn't the issue, but where th game was played was.