I didn’t really have such a hobby back then. I’ve definitely done reading a paper book as extensive reading and looking the word up on my phone. I would follow some rule that I can’t look up a word in a dictionary unless I’ve failed to understand its meaning several times in a row. The slow part was that I’d have to unlock my phone all the time, so if I was to do this, it would be faster to read next to your computer with the dictionary tab open.
As to how efficient LingQ is compared to paper books, as others discussed in the Is extensive or intensive reading faster for vocabulary acquisition? thread, it depends. My conclusion from the thread was the ‘semi-intensive’ reading is more efficient for vocabulary acquitision, but only if you can reduce the faff, such as flipping through a paper dictionary and reducing the digital equivalent on LingQ or whatever other software you use.
That said, vocabulary acquisition isn’t always your primary goal, especially as you become advanced in the language. You are more focusing on soldifying the words you already know, learning the nuiances of the words, which is only possible with lots of exposure, and other goals, etc. This may mean you are reading texts with a high amount of known words and very little need to look things up in the dictionary. For example, if you know 99%+ of the words in a given text, what benefit do you get from studying it on LingQ?
Firstly, I would use books specifically designed for language learners, such as those with key vocabulary in the margins and bilingual readers. If that’s not an option, I’d be very selective in what I read to make sure that I have very high comprehension (the magical 98%, which everyone loves to quote) and do mainly extensive reading, only looking up the very occassional word in the dictionary, if I encountered it many times in a row and still didn’t know the definition. But if I had the option, I’d throw out the paper dictionary and instead have an advanced/native speaker next to me as a ‘verbal dictionary’ to ask “What does X mean?” This would have much less faff than using both a paper dictionary and using LingQ. Alas, it’s not easy to get a cheap ‘verbal dictionary’.