Yes Switch has risen, peaked and declined (like almost every other platform), but that doesn't mean the sales curve is the same. GBA, PS1 and PS2 for example all peaked in FY3, but their sales curves are very different.
If you compare Switch's FY5 sales to its FY2 sales, and then do that for every other Nintendo platform, you will see that Switch's curve is very different to everything else except the DS. This is due to a combination of Nintendo focusing all their development resources on one platform, and the impact of the pandemic. At this point in its life the DS had already had its successor announced, and for Switch this hasn't happened.
Switch could have longer legs than the DS, depending on when the successor will be revealed and released.
Yes, every curve is obviously are different: peak taller or shorter, in a year or in another, a longer or shorter tail, different types of overlap with their other gens, different types of mid gen bumps (revisions, Pro versions, price cuts) etc.
In fact if we want to group them, by more or less types, there would be the sony home console ones (with a way longer tail with a long overlap during generations), the Nintendo home consoles except Wii (shorter curve/lifecycle with little intergenerational overlap) and Nintendo portables + Wii (somewhere in between).
What I meant is that all have in common these stages of growing, peak and sunset, and that Switch is in the start of its sunset stage (so we should expect yearly decline in YoY yearly sales), while PS5 and Series are in the growth stage (yearly growth YoY, specially because got badly affected by shortages).
I have to update my doc where I had all the curves with the numbers of Swith, PS4 and PS5, and I don't remember everything. What I remember is that if you adjusted their difference in quarters because of being released in different parts of the year, Switch was repeating almost exactly the curve of PS4, to the point that Nintendo placed the PS4 sales for that year and did work until the year where they expected to start the decline, but covid bump happed.
This caused the peak to be taller and longer, making it more similar to other type which as of now I don't remember (it could be the DS as you mention). In fact I'll go to update the graph.