If we’re talking about that climb up and through Toro Canyon, that’s a legit climb by my standards, measuring 1.36mi at an average of 5.3%, and .6mi of it averaging 7.7% with kickers in the double-digits, up to 15%.
Since the OP had the gearing for it, I’d say this is about two things: pacing and learning to suffer better.
I say pacing, but of course have no idea what the OP’s strategy was, however, not having a heart rate monitor suggests it might have been easy to overextend on previous sections of the ride (due to excitement, feeling good, etc.) and simply hitting Toro on a too-empty tank. Again, that’s speculation; it could have been going to hard on the run-up to the climb, or it might not have been an issue at all, but without an HR monitoring, we can’t really say.
“Learning to suffer” essentially means persevering at the most difficult times, like wobbling up a 15% pitch at max effort. I think the real key is confidence, that courage which comes from having been there before and knowing you can make it, but there are also mental and physical strategies one can use to push aside the pain and fear, find a way to relax a bit, and get in those few extra pedal strokes it might take to get over a hump. That can be telling yourself “you got this!” and focusing for a few seconds on controlling deep breaths and feeling calm, or maybe it’s consciously relaxing your shoulders and figuratively settling into the pain of the effort, rather than trying to force your way through it.
I dunno…I’m a heavy rider and I find I have to go through all sorts of pain and tricks to get up stuff lighter people seem to hardly notice. That said, I’m not a bad climber, at least to the extent that although I’m usually the heaviest, I’m never the slowest! My point here to the OP is to give encouragement that, regardless of weight or current fitness, they can improve their climbing, and in practicing it, they’ll get stronger and fitter and more comfortable suffering, and at some point, hills which were once a struggle will get a lot easier.