Well, competing at a satisfying level with people who have more twitch then you is hard at the beginning - I'm in my mid-30ies and I have no delusions that my reaction speed per se is starting on an equal base with some young teenager.
Practice is the only answer here though. I started arena on my pallie with a lock, taking over from a server transferee. The team rating was 1440 at that time, after our first ten games we were at 1382. The following week we dropped as low as 1320ish before ending around 1356 or so. But after that, we started climbing back up step after step, and are now sitting at 1632.
Matter of fact, until you reach the gear limit (full epixed out), you're still competing a mix of gear AND skill, so some weaknesses in coordination can be compensated for with better kit, and the rest, well, practice, practice and more practice. Skirmishes are a good way to warm up to the hectical pace before starting ranked games on an evening, but they aren't really proper training grounds, for several reasons:
1) You don't feel the appropriate level of pressure. There's no consequences to losing and you have nothing to gain by winning.
2) The matchmaking system doesn't work on Skirmishes. You can play against your battlegroups' underdogs and crush them, and the next skirmish you're pitted against the Rank #1 team doing their own warm-up.
Nothing beats the real thing, so you're going to have to go out there, bite the dust, see your ratings tank for a while, and you will eventually start to learn valuable lessons, many of which don't have too much to do with speed of button-clicking but rather rapid evaluation: When to bubble, when to trink, when to cleanse, standing to heal, moving to break LoS, stun, torrent, toss a quick holy Shock, bless protection or freedom...
At first the important part won't be that you lost a game, but rather that you learn to identify at what moment you lost it, drawing the lessons from that, and trying to avoid repeating the same mistake in a similar situation.
After a while, you'll get used to it AND teamwork with your arena partners, and that's when you start climbing in ratings again. Also, if worst came to worst, you could always disband the team, buy a new charter, and start over.
Back to the subject of automation, though. Before Patch 2.0, I had my first pallie soloed to level 26. One of my guildies needed a hand with an alt in VC, and I was asked to heal.
Back in the day, I had an absolutely great pallie add-on. It would bless classes according to rules I had set, warn me of reblessing, but beyond that, it would also handle all healing at the press of a button. And I mean all of it. Selecting which spell to cast, which rank, and most importantly, who to cast it on. We made it to Van Cleef while I constantly pressed one single button without a clue in the world as to what I was actually doing.
Needless to say, when I made my current (and final) belfadin, I wasn't just utterly clueless about healing, I was also scared witless about it.
The removal of all automation gave me a lot of work to do, but I do believe that I'm a better pallie for it.