i have to agree with the point of picking your strength and playing it constantly.
the more you play it the more you can hone it. the more you can understand it. the more you'll learn what works against it too. it'll end your losing streaks over time for sure if you're analyzing things correctly and adjusting. from those experiences you can then learn what makes other archetypes viable as you lose to them. for example: if you're playing aggro and keep losing to control, as your aggro play gets stronger and you start beating those decks, youll start understanding what makes those decks work. this means when you want to try something different you'll have a greater understanding of how to play that archetype right out of the gate. in turn this means you don't have to repeat the entire process to the same degree all over again. from this you can develop breadth of experience and knowledge. jumping around from archetype/deck to archetype/deck without mastering any really just makes you a sloppy player. it doesn't hone your skills or make you understand why something actually works or doesn't work. you're more likely to just get frustrated by losing, and you wont' necessarily have the skills yet to do more than that.
i agree it does sound like he's just a better player.
my advice is talk to him after games, and during games. leverage him for information to try and improve your own gameplay. ask him why he might make one choice over another. ask him what improvements he'd make to your decks. discuss things. it makes a huge difference. the game should really be a conversation. in my own group we tend to talk about what worked and what didn't. what might have been a better play and why. in the moment sometimes too. its helped improve everyone's gameplay dramatically. in some cases its really improved deck construction for players on a budget by finding better cheap alternatives, or taught netdeckers how to actually pilot their builds. in general its just elevated everyone's ability and most of us are now on an even keel.
its been my experience that most people who win a lot love talking about the game and the experience with the people they play with. no one wants to win all the time. you get bored and want to be challenged, so you start teaching when asked.