One thing I will say is that Nintendo doesn't necessarily need to match the output they had in previous generations because they aren't supporting two, very distinct consoles anymore.
As the sales numbers comparing the handheld and home console sales numbers of each generation showed, most people were not buying both (the closest I think it would be off the topic of my head is probably the Wii/DS generation) and so Nintendo needed to have games releasing on both to support different audiences. This meant, opposed to now where we consider a good month to usually have one, pretty solid Switch release, Nintendo needed to release more than that to support both consoles.
If the handheld and home console every generation had very comparable sales numbers and Nintendo has evidence that it was somewhat because owners of one would pick up another, this would've been less of an issue since they would only need to appeal to one, larger audience. However, with the audiences being more split, Nintendo needed to have releases ready for both consoles to show their support of them. To me, this is shown in the fact that the 3DS/Wii U generation had days where multiple first-party games released between both consoles (2014 being the most memorable to me because I bought Pokémon Alpha Sapphire alongside Super Smash Bros. for Wii U on the same day). In many of these examples, now on the Switch, this wouldn't happen, especially multiple big name games launching because they are on different platforms.
If Nintendo still were doing two consoles per generation, we may have seen a 2D Zelda by now that released on the handheld, likely in similar proximity to another larger title that would've released on the home console. However, since they aren't split anymore, for a holiday season that might've had the 2D Zelda for the handheld and Metroid Prime 4 for the home console, they don't need to do that anymore. Now, they can space them out much more, while also working on the handheld games to match what a home console experience may be like (Samus Returns on the 3DS to Metroid Dread on the Switch is probably the best example I have). This also means that franchises that would've been frequent on one or the other may now become less frequent because Nintendo doesn't need multiple games a month (for multiple consoles), even if some months do end up that way still now.
I would also just say that the way some of these franchises are approached now is just different. As mentioned earlier, there is no longer a need for there to be two Golf or Tennis games within a single generation from Nintendo just so they could have them on both platforms. However, like with Pokémon, they aren't releasing third versions anymore and, instead, electing for DLC, which in itself will somewhat lower the amount of first-party Switch games since even when they release a package with the base game and all the DLC, it is priced as the base game + DLC opposed to how the third versions would've been priced the same as the originals.
In a lot of ways, before the Wii U, I was much more so the handheld gamer, where, while my family was fortunate enough to have the Nintendo home consoles, my older brother typically would be the one that purchased the games for it and played on it more often than not (mainly the Wii). This meant for me, I was mainly focused on buying DS games, which then Nintendo needed to have both games I could buy on the market and ones that my brother could buy at the same time because we were two different audiences. With the Switch that doesn't need to happen anymore, which will inherently lower the amount of games Nintendo needs to release monthly/quarterly and instead they just need to focus on having a constant release pipeline for the console, with all their teams on board. I don't think it would've been feasible for Nintendo to move from two to one and still have the same output as, even if they are at the scale they would've been at the 3DS, they still require a lot effort as they are HD products, something that I think is seen with how Nintendo couldn't have the constant schedule with the Wii U that it needed. There's more expectations now when you have your game release on an HD console that the DS/3DS games didn't need to have.
Finally, I think we have seen this throughout this generation honestly. We do have games now that likely would've been handheld games if Nintendo kept to this format but are used to bridge the gap between Nintendo's larger sellers. Making this post did make me realize that it was probably really smart for Nintendo to move away from the two consoles strategy to the one console as, for the way they make games, eventually these two strategies wouldn't be able to complement each other like they used to as the hardware between the two platforms would've continued to become more and more similar.
I apologize with the length of this post and how I did repeat myself a lot throughout it.
The TDLR of all of this would be that: I do feel like the combination that even smaller scale games (which I feel like still makes up a good amount of the first-party library) requiring more resources to be on the Switch and the fact that Nintendo doesn't need to support multiple platforms at once does mean that it isn't really feasible to expect them to match the output of past generations (as much as I would love for them to be able to!)! I feel like, ultimately, the Switch has had constant releases, both larger and smaller scale titles, which makes getting the newest Nintendo game up to ones taste now opposed to having to get it because of the platform that you mainly use. I do understand that not every Nintendo release during the year will be able to draw everyone in, which does make years less appealing, which may have not been the case previously since, especially in the Wii/DS era, if you had both, you did have more of a choice. I don't really think this is inherently Nintendo's fault as they don't want to flood the market with their own releases. In fact, I think this has allowed them to be more careful since we know they sit on titles, something that likely is an outcome of the consolidation of their studios, because they don't want to flood their own market. It just means that titles we probably would've seen more of by now, mainly from the handheld side (2D Zelda's, titles like Kid Icarus Uprising) have to coexist alongside traditional home console experiences (3D Mario and Zelda) on the same console opposed to different ones, meaning that the constant release of titles will pull from both types of experiences opposed to one.
I'm sorry again for the length of this post!!