OP the reason you likely have more success with offbeats at your current level, or to be more precise at your opponents current level, is that in more mainstream stuff they play book moves, then when the book finishes, they play at their level. So in a sense the true level in tactics, positional understanding etc is put under the carpet because of the opening.
Not giving too much focus on the opening phase is right ando some offbeats can be fine and sound but tbh 1. e4 or 1. d4 will teach you more, after that you can go back to offbeats or playing a mix of mainstream and offbeats.
Perhaps play a small repertoire with 1.e4 ( or 1.d4 ) 1. e4 e5 and 1. d4 d5. Especially the open games are important to understand.
There are some good repertoire books which are actually very playable and they're just 200 pages long.
It's good to play a bit the open games and have some thematic pawn structures in your games.
If we are comparing it to languages then it depends on the languages. It's possible to study multiple languages at once, if one wishes to, and it makes it easier if they are related. Learning Spanish will give you some basis in Portuguese, Italian and French. Learning Russian will give you some basis in Ukrainian, Polish, Slovak, etc.
Also no-one expects someone to have learned a language for 1-2 months and start speaking it perfectly. You have to start practising, improvising and learning from mistakes.
With openings, you can't be expected to memorise every single line in e4 or d4. If everyone could do that easily then chess would be closer to solved and it wouldn't be such a competition. No-one starts playing e4 or d4 because they memorised every line or play perfectly. Sometimes you have to improvise and think to figure things out.
I play Ruy Lopez, Najdorf, Open Sicilian and King's Indian. That's not because I know all the theory but because I enjoy those openings and learn by playing them. The opponents don't know any more theory than I do.