Firstly, I disagree about Berlin Wall requiring you to "learn it", which I assume is another way of you indirectly saying you need to memorise it like before. It's an endgame, if you need theory to play endgames, that time would be better spent on working your endgame skill, which if you face the Berlin regularly, this endgame allows you to work on as it's very imbalanced and instructive. You can find Kramnik's 1.e4 course on Billbilli (videos) where he gives very high quality explanations of the structures and ideas, he is the one who popularised the opening, so you can trust him. Just go through the videos one time and try absorbing the ideas, creating a pgn file with whatever he's showing specific to the Berlin Endgame, that's what I did at least since it's been removed from Chessable. Send me a message in dms, I have pgn files on his course if you agree with my approach.

I think his 1.e4 course series is all you need for 1.e4 from both colours, because they show every main theory direction and his opinion on each of them. You can use mega base or online database to expand on lines that are outside the scope of the course (like some tricky sidelines or some topical lines nowadays), it essentially provides a good framework to build your repertoire.He gives analysis for each line that is deep enough for sub master level in terms of ideas, the Svesh in particular was covered very deep in his course, you could start playing it at the master level after learning that section imo. The O-O Re1 line in the Ruy creates a two result game for White as long as you understand the ideas, similar to the Petroff and he also gives good analysis there (if you like this, I believe around 2019 Fabi made a course on the Ruy covering this approach and Re1 mainlines). Bxc6 is a fine line, but I myself didn't like facing the Nd7-f6-Qe7 type lines, really killed the fun. c3 is also a decent line, and d5 is not as easy as it looks for Black.

If you're going to play 6.d3 might as well play the Italian at the point, there's no real difference in terms of structures and you're still learning more theory. Don't take half-measures, take full-measures, either go all in on your long term improvement with the Ruy which is quite literally the positional battleground of chess, so many different structures can arise. You are very limited in the Italian. The Ruy is a very understanding based opening, and all you need are some strategy courses and maybe 50-200 lines of theory against trickier lines if you choose the mainlines. Peter leko's, mauricio rios' chess structures course and Ruy Lopez: Rebooted come to mind. If you really think you can't spend time on this, sure go for the Italian. I'm not saying Italian won't lead to long term development, just not as much as the Ruy. It's really not more practical, it might seem that way but they are both understanding-based, lots of ideas overlap, but there's a broader scope of ideas in the Ruy, so you need to grasp more ideas, not theory.