So, what does that mean? It means that if you start today and played continuously for 10,000 hours, you would be a concert-ready expert in just over 416 days!!!!
If you practice 5 hours per day, you'd be an expert sometime during April of the fifth year.
Whether on guitar or piano, I sometimes worked on a piece to get it perfect, only to hate it by the time I got it there. Someone posted somewhere that perfectionists make for unhappy musicians. I'm sort of taking that to heart. This time around with the guitar I'm really focusing on the theory and truly mastering the scales and modes so that I don't have to worry about perfecting every note. (I no longer play classical guitar which demands perfection.) It's like a professional drivers/racers: They've been trained to know how to get themselves out of trouble. I will no longer ruin my music by worrying about being perfect. It takes the fun out of the playing.
So, the answer? It depends on how you define mastery. If you spend 20 hours pefecting one piece of music and are bored, then spending 100 hours perfecting five pieces of music won't necessarily return a different result. Maybe instead you accept that it's "good enough" this time around then come back to it later to take it to another level? It's all a state of mind. I'm not advocating mediocrity. I'm just suggesting that if you're playing to the point where you're bored you might want to recalibrate your practicing philosophy. Music making is supposed to be fun.
OMG! As you already know, there are seemingly countless web resources and books out there appealing to guitar players. From my experience, they all offer the same menu, but seem to cook it a little differently. It all comes down, therefore, to your taste--How you learn. What may seem dry and unpalatable on one site, will scintillate your senses on another. There is no way I'm qualified (or anyone else for that matter) to make a recommendation that will work for you.
So what to do? We don't have enough time to try everything or every teacher, so what I do is sort of rely on what seems to be working for the masses. For books, I do web searches for reviews but I also read the user reviews on Amazon.com. I give particular attention to those that have the highest rating that have been reviewed the most times. I also check out who is giving the highest reviews to be sure they aren't publisher agents, as best I can.
Anyway, there are two books I use that have received overall pretty good reviews:
"Guitar Fretboard Workbook" by Barrett Tagliarino and "Guitar Aerobics: A 52-Week, One-lick-per-day Workout Program for Developing, Improving and Maintaining Guitar Technique" by Troy Nelson.
I'm sure--and hope--others will join in and offer more, but two more points: First, the guitarists who can really play that I know got there by spending hours and hours working on scales and modes.
Second, regarding perfecting your music, I forgot to mention/repeat what you have doubtless read everywhere else and something that is very hard to do--slow it down. You are hardwiring your brain to direct your fingers, hands and arms to perform some extremely complex tasks. It's very easy to program it to perform the wrong tasks. If you rush through a piece, your brain will remember and hardwire all mistakes.
I read somewhere that when composer and pianist Sergei Vasilievich Rachmaninoff was preparing for a concert, he played each note in a concerto extremely slowly and deliberately to ensure each movement was "wired" correctly. If the masters do it, then what makes us so special? Something I have to continue to tell myself.
Anyway, enjoy and keep sharing.