Well, you need an always-online node only if you actually need it to be syncing all of the time. Not everyone needs this; often times it's enough to just sync opportunistically. This is mainly necessary for things that are mutable and active; for me, I store my Keepass XC on a Syncthing shared folder, so this is relevant to me. And for that, I use my NAS, although obviously, not everyone has a NAS.
But that's the thing. Especially notable compared to NextCloud, Syncthing is not like most "self-hosted" software. Because a node is a node is a node, and because it's relatively lightweight, it literally doesn't matter what you use. You can use a Raspberry Pi, an old phone or laptop, anything you can connect sufficient disk and a network to can be a Syncthing node. And if it catches on fire, it doesn't really matter since every node is equal. You can just add another node at any time.
So a lot of people think Syncthing is another thing you'll have to worry about and maintain, but it's not. It's one of the few pieces of software that I expected to have to deal with a lot of extra work to use, but then it wound up being dramatically easier and more flexible than I expected. I worry about robustness when it comes to something as complex as cross filesystem syncing, but Syncthing has never lost my data. I have backups turned on on most nodes for the important folders, but I've never consulted them before, because I've never needed to.
Surely it is possible to lose data with Syncthing, or otherwise create a headache. However, from my point of view, it certainly seems to be among the most reliable and lowest effort ways to sync stuff across devices. I haven't had to spend almost any time maintaining Syncthing, and I don't have to worry about limits. I just need one device with a big enough disk, then I can create however many shared folders are needed to get the granularity I want.
Syncthing also has a pretty cool encryption feature. It is considered "beta" still, so I only use it in "trusted" scenarios, but it works great.
When I started using Syncthing, I only intended to share some document files between my desktop and my laptop. Now I use it to sync my Keepass database, files between some servers (think seedbox etc.,) multiple different documents folders including some for collaborative projects, and even a couple of other things. So it really wound up over-delivering for me.
I'd strongly recommend people, even people who already feel like Resilio Sync wasn't a good fit, to just try to set up Syncthing before resigning to Dropbox. Comparatively, I think Syncthing is simpler to use and more robust than basically any other solution that isn't Dropbox.