This is a tough question to answer because there are more songs, genres, styles, techniques or personal approaches to the guitar in existence than one could realistically master in a lifetime.
Difficulty is also a hard thing to define. Some people find “intermediate” examples to be extremely easy, while others find them very hard to master. So it is with “beginner”, “intermediate” or even “advanced” techniques. What one person finds hard isn’t necessarily hard for another, and what one person finds easy isn’t necessarily easy for another.
There also isn’t necessarily a logical progression or roadmap for becoming a better guitar player. One student might delve into method books while another learns simple Green Day songs, and they could both grow to become equally great players. In essence, one method isn’t really better than the other.
Technique and Finger Strength
Developing proper technique and finger strength is usually where a lot of the “grinding” work lies for guitarists. A guitar player has to learn how to pick and strum with their right hand, and how to coordinate said motions.
They have to teach their left hand fingers where to go in what sequence on the fretboard, how much pressure to apply, how much each finger needs to be arched in order to achieve a clean sound, and so on. From bending and hammering-on to chord formations and scales, guitarists have a significant amount of work cut out for them in this regard.
The right hand is often the “forgotten” part of guitar playing, as most players learn the basics of picking and strumming within a very short amount of time, but this isn’t to say that there aren’t other advanced right-hand techniques either.
The secret to fast-tracking this process is repetition. By repeatedly doing the right things over and over, guitarists can quickly build up muscle memory and get to the point where they can do the right things without even thinking about it.
Theory and Knowledge
Technically, it is possible to play any instrument without any training in theory. However, guitar is perhaps the most dominant example of an instrument that doesn’t necessarily require a solid footing in music theory to be able to play well. Just look at Jimi Hendrix.
Therefore, guitarists don’t really need to spend a lot of time learning theory to be able to play their instrument. There can be many advantages to doing so, however.
At a most basic level, what guitarists need to know is how their instrument works, what tools they need to be able to play it, and what role each hand plays in the process.
What level do you aspire to? Learning to play a few songs by the campfire will require a different kind of commitment than learning to play like your favorite guitar heroes.
Pursuing virtuosity on any instrument takes a significant amount of time and dedication. In this regard, one isn’t necessarily harder than the other.
How much time do you realistically have to practice? Can you commit to practicing every single day? Can you push through the initial challenges of awkwardness? All of these points will play a part in how hard (or easy) it is for you to learn to play the guitar.