here is my off the bat very brief analysis of both Harry and Louis' albums:
there are obvious connections... in the way that ready, steady, go! sounds like it could've fit right into HDIGH, and similarities between the way the albums were produced. thematically, though, the word that keeps coming to mind when I think of both of their albums is time.
it's clear that both Harry and Louis have pushed themselves into new spaces whilst developing these albums. both of these albums show an idea of progression and evolution. growing up, side by side.
Louis starts his (vinyl) album with the sound of a clock ticking, even singing in All These Skies that "time stands still" when he's with his person, or "thinking of ways that we can pass the time", in Lazy.
meanwhile, Harry calls back in Pop by saying "I wanna take up all your time". or better yet, in Coming Up Roses with his line "I've turned back the clocks". harry even ends the album with the encouraging words of "it's all waiting there for you".
remember how Harry said one of his biggest fears was wasted time? prior to Louis' album, had you ever asked yourself the question, how did I get here? it's usually linked with the lack of staying grounded, losing track of time that's passed in your life.
not even to mention visually how the two are linked - with Louis walking on treadmills for each of his visualisers, and Harry's use of stunt doubles for driving/biking/running etc. as well as the actual clock, counting down on his website.
anyways.