I don't really understand why you're using Vita as an example of late cycle major publisher support? I mean it got some but even compared to 3DS it didn't really come out ahead at all when you look at what both actually received. Post Switch support from both for the Big 5:
Bandai Namco 3DS
- Dragon Ball Heroes: Ultimate Mission X
- Neko-Tomo
- Pro Yakyuu Famista Climax
- Tamagotchi no Puchi Puchi Omisechi: Ninki no Omise Atsume Maseta
Bandai Namco Vita
- Accel World vs. Sword Art Online: Millennium Twilight
- Digimon Story: Cyber Sleuth - Hacker's Memory
- Gintama Ranbu
- IDOLiSH7 Twelve Fantasia!
- Super Robot Taisen X
- Tsukitomo: Tsukiuta 12 Memories
Capcom 3DS
- Apollo Justice: Ace Attorney
- Dai Gyakuten Saiban 2: Naruhodou Ryuunosuke no Kakugo
- Monster Hunter Generations Ultimate
Capcom Vita
Konami 3DS
- 100% Pascal Sensei: Kanpeki Paint Bombers
- PriPri Chi-chan! PriPri DecoRoom!
Konami Vita
- Jikkyou Powerful Pro Yakyuu 2018
- Pro Yakyuu Spirits 2019
Sega 3DS
- Etrian Mystery Dungeon 2
- Etrian Odyssey Nexus
- Persona Q2: New Cinema Labyrinth
- Radiant Historia: Perfect Chronology
- Shin Megami Tensei: Strange Journey Redux
Sega Vita
- Catherine: Full Body
- Persona 3: Dancing in Moonlight
- Persona 5: Dancing in Starlight
- Toaru Majutsu no Virtual-On
Square Enix 3DS
- Dragon Quest (digital only)
- Dragon Quest II: Luminaries of the Legendary Line (digital only)
- Dragon Quest III: The Seeds of Salvation (digital only)
- Dragon Quest XI: Echoes of an Elusive Age
- Pictologica Final Fantasy (digital only)
Square Enix Vita
- Itadaki Street: Dragon Quest & Final Fantasy 30th Anniversary
- Romancing SaGa 3 (digital only)
- Secret of Mana
I think it's fair to question Nintendo's ability to extend Switch's lifecycle outside the 5-6 year norm, which is something they haven't really done with their successful post millennium consoles (GBA, DS, Wii, 3DS). Before that though they did do it, as the standard really (FC, GB, SFC).
I think the "3rd party issue" is a less pressing component of that though because, unlike most/all of Nintendo's previous consoles, Switch is fully looped into multiplatform development and gets heavy mid tier, niche and indie/doujin support. Switch will be getting 3rd party releases for 5+ more years and on the whole it's late cycle support will look a hell of a lot better than Vita or 3DS.