The thing is, I think the whole market is tilted towards wheels that are as light as possible and hence, margin of strength is not what it could be. And the focus of this issue is naturally the rear wheel, because it carries more load, yet is weaker due to being dished. The ways to alleviate this relative weakness, relative to the front wheel, not to mention the rest of the bike are:
-stiffer rim
-less dish
-wider hub
-more spoke tension, while staying within the respective limitations of the rim, the spokes, and the hub

BTW, by more spoke tension, you should understand, more cumulative spoke tension. In other words, more tension on a given number of spokes, or, the same tension on an increased number of spokes.

There aren't too many practical ways to reduce dish or widen the hub (i.e. with a wider replacement); but they might be worth pursuing if you're after every advantage.

Of course it is assumed that the wheel is built properly with appropriate & even spoke tension. Failing that, strength is naturally compromised.

To sum up, the one part of the typical road bike I wouldn't hesitate to add a few ounces to (and spend a few bucks) in order to gain some strength, is the rear wheel.