as far as pvp and my stam warden - i dedicate all my stamina pool for doing damage...

I focus my magicka use on shields (ice fortress), and heals (enchanted growth)...i also make sure to slot healing thicket on one of my bars...

wardens (both mag & stam) are really durable characters...

https://forums.elderscrollsonline.com/en/discussion/comment/4541471/#Comment_4541471

If you look at trials builds, you typically see a magicka templar and a magicka warden. Most of their major healing abilities work off of magicka. Resto staff healing abilities are also important additions to the healing arsenal and those use magicka. The two healers in a trial are dedicated healers, whereas most stamina heals are more limited.

That being said, a stam warden pure healer could definitely be viable. You are going to have to practice a lot with it for harder content. You'll be fine in normal dungeons simply because most builds are, but normal dungeons will be a great place to practice because your teammates will stand in mechanics that they shouldn't and your tanks may or may not be squishy. Healing random players through dungeons is a great stress test for a healer build.

Veteran Dungeons will take more work and practice. In my experience with warden healers, you'll have to make sure that your group stays topped off with lots of heals over time, because you won't have the Breath of Life skill from Templars or even the spammable skills from the resto staff. I can't say whether it will work or not because in my experience you don't need to have a perfect build to PUG veteran dungeons either. You do need to know what you are doing with your build. A stam warden pure healer might be perfectly able to complete veteran dungeons, but it will be significantly harder than completing with a magicka warden or templar healer. Now, if you have a good group that you run with, I'd expect your stamina warden healer to do fine.

For trials, unless you want to PUG trials, you pretty much run what your trials group wants you to run, with the obvious caveat that if someone can complete the content with whatever off-meta build they have, that's their right to use whatever works. I'd be surprised if a stamina healer could output enough healing to outperform a mag warden or mag templar enough that a trials group would trade out one of the normal healers for a stam healer. If this is the level of content you are aiming for, I'm not going to make any bones about it. You'll have to get good with your stam warden healer. Once you've proven that you can complete trials though, it should get easier.

For PVP, because you absolutely need Vigor from the assault skill line as a stamina healer, stamina heals are super nice when dealing with Negates. Once a Negate gets thrown on a group, all the magick people are useless and its the stamina heals that save the day.

A build I saw:
https://forums.elderscrollsonline.com/en/discussion/349045/yffres-guardian-stamina-warden-pve-healer-morrowind https://www.reddit.com/r/elderscrollsonline/comments/6hju4q/stam_warden_healer_now_vaa_approved/ (Someone who did complete a vet trial with one, so it is possible).