That is not true. Nintendo EPD output lately has been abysmal. What have they made for the Switch? BOTW which was just a Wii U game delayed for their next system. Mario Odyssey, Mario Maker 2 and Splatoon 2. Those are the only well received ones barring those they’ve made Arms, 1-2 Switch, Labo. That’s it.
With 11 teams and given how small scale most of Nintendo’s games are we should expect a lot more. I mean these guys aren’t making huge games with cutting edge visuals and detail that they need 3-5 years to put out a game.
You're also forgetting Sushi Striker (Which is an EPD creation co-developed with indieszero), and Animal Crossing New Horizons, as well as Ring Fit Adventure.
You have to remember that Nintendo typically focuses of the first 2-3 years of a console's life for the first wave of software for a new system, that plus the fact that most of their staff was consumed by BotW at that time, so it often takes a while for new projects to start up after such a big release.
Also Nintendo's internal teams have never been the majority of the company's yearly output, even before the Switch, EAD and SPD together have only ever put out 4-5 games a year. Besides, EPD doesn't just do internal R&D, they also have oversight of all of Nintendo's externally developed games too, so they have more responsibilities beyond just making the next Mario and Zelda.