As an amateur southpaw, don't let it discourage you :)

Currently 91kg (201.6lbs) and 194cm (6ft4)

I won't lie, we get a massive advantage as boxers until we enter the pro scene, because like you said you rarely find a southpaw. I'm going through a training program right now with about 30 other students and am only one of 2 southpaws in the gym. The benefit of this is not only do we get to use our own style, but we usually spend an enourmous amount of time practicing counters for regular as well as often practicing regular stance itself.

is it unfair? Maybe. Is it something to let discourage you? Absolutely not! Be proud that you had thebexperience, and learn from it the best you can. A good boxer is made of his practice and his skill, an amazing boxer uses those skills to win in any scenario.

However even an amazing boxer will lose to a southpaw if they have no prior experience, and no practice. Since your left is your Jab, a little secret is to practice countering our right jab. Am just above anf to the outside of their jab as they throw it and come up and around, aiming for the corner of their defence where the shoulder comes up to shield the face. If you land a shot there it's a great way to get their head and rattle them for a bit.

if anything, take advantage of fightng southpaws whenever you can and just practice practice practice, you'd be surprised how much of those spar sessions will give you new moves in regular sessions as well.

As for him seeing so skilled, I wouldn't worry about it. Regardless of training and ability, due to tue nature of the southpaw stance, it provides us with some unnatural angles so until you learnnto defend against those punches it will always seem they are hitting you more or that you're not blocking ahots well or fast enough. But that's not necessarily you, it's due to the openings our stance gives us.

All the best, and keep it up! Feel free to ask any questions :)