Michael Daly wrote:

I've met folks both with and without formal training and they can have
both good and bad technique. Add to this that paddling technique has
been in a state of flux, to some extent, recently and you get all sorts
of techniques being taught with no clear idea (for the student) of what
is right.

Another problem is that most racing is short distance (Olympic C and K)
and those techniques are inappropriate for long distance or recreation.

Exactly. Frank Healy mentioned 90 degree feather as being standard,
but for long distance and recreational paddling, it was long ago decided
that this extreme angle exacerbates RSI (repetitive stress injuries)
so feather angles moved to 75, then 60, and now 45 or less. A worthwhile
tradeoff of increased wind resistance for less likelihood of RSI.

For whitewater sometimes you need a big blade to get in a quick stroke
to stay on-line. Also in whitewater, some blade designs perform better
for backpaddling than others, a trait racers needn't worry about.

It's an interesting datapoint that racers are NOT using bent shaft...