I'm asking because it's my understanding is that the gains I made in a year have somewhat peaked, and progress from now on will be much slower because I started out at such a weak, frail, pathetic standard.
That wouldn't have changed. You're a year ahead of where you would be if you started now. Everyone gets their noob gains in the first year or two and then it stops. If you had started now, then a year from now you'd slow down like you are today.
Looking back, I'm wondering if I should have just focused on eating enough to gain to where I am now and then start working out.
If you had done that, then you'd have more body fat than you have now. Instead you're at a healthier weight with more muscle and less fat. That overall makes you a healthier person.
What would be the best way to optimize results? Focus on eating big with light exercises, or go full on with strength training and eating big at the same time?
There's no advantage to gaining a lot of fat unless you're bodyfat percentage is already at an extraordinarily low levels which you most likely are not (if you were at that point then medical intervention may be more necessary which we're not qualified to give advice on). So you shouldn't focus on eating massive quantities of food for eating's sake. You should eat just enough to gain a little bit of weight. If your weight is slowly trending up over time (<1kg a month), then you're in a sweet spot. If your weight just jumps 5kg in a month, then pull back.
I would say there's no disadvantage to full strength training. It takes time to learn, practice, and grow so starting now is better than starting tomorrow. My only regret in starting strength training was I didn't start sooner. Had I started sooner, I would have regretted not starting sooner than that.
My thinking is, if I had gone from x kgs to x+6 by just healthy bulking and then started working out, my overall progress would probably result in a weight of x+6 + , which would be relatively far more impressive.
Right now you're x+8. A year from now, you'll be x + 8 + <gains from another year's worth of strength training>. That's far more impressive than this example.
An 8kg increase in a year is good. You should be proud.