I feel like everyone else has said everything I would in regards to the battle advice aspect of your question, but maybe for some general battle advice:
-Yozora has two separate types of attack "colors", red and blue. When he uses a blue attack you cannot block it with guard. At all. It will go straight through. Very often with his laser beams he will alternate with something like red, red, blue, red...etc. This means you can't just stand there and guard through them all because the blue one will 100% hit you and then generally chain into forcing you to get hit by the next red laser as well. So, either you need to get into the habit of alternating your defense so that you do something like block, block, dodge roll, block OR just dodge roll from all of them.
-Every single one of his attacks has a set timing. Are you a musician at all by chance? Very often I find with his fight the best thing to do was to keep an internal "beat" going in my head for every one of his moves. For example, one of his attacks he will freeze, pull his blade back behind him to "charge" it (and at this point the blade glows either red or blue). I found during this, the safest method to survive for me was to literally just time it. Just before he attacks there is a brief flash of light that tries to trick you into blocking early, but you actually have to guard/roll a second AFTER the flash. So in my experience there was always, exactly enough time for me to think in my head: tick, tick, tick, flash, BLOCK (or roll, if it was a blue light). I would say this out loud sometimes until I internalized it.
The same applies to the pyramid "cage" he traps you in. Not only does each one have a very distinct, set "time" after he traps you when you can roll out of it, if you have mp you can get a very very easy combo off on him here just by casting thunder because it stuns him and you should be close enough to just hit him right after. You can also break out of these just by using a transformation if you have one stocked.
Here is my actual recommendation: do not play the fight to win. Just don't. Don't even play the fight to hit him. The first handful or so times I battled this guy I was 100% on the defensive, learning exactly how to dodge every single one of the moves I could see. I never tried to hit him at all, ever. The point was to learn exactly when and how to avoid getting hit. Once i learned the timing on his attacks, and it was all practice, I was able to find windows to attack him. If you don't feel like trial and erroring how to dodge the attacks yourself, definitely do what others recommended and look up the videos showing you the steps and then just practice doing what they do.
Seriously. Defense is your best offense here. When I first beat him that is 100% the strategy I used: I learned how to dodge/block/survive most things, found 2 - 3 openings of his during attacks I felt the most comfortable with where I could damage him back and then just survived, rolling around like an idiot the rest of the time until those attack windows came back up again and I just slowly wore him down. It wasn't the most elegant victory, but it certainly worked and it was far less stressful I think in the end than going into it feeling like every death was a "failure" because I could tell myself "hey, I am not trying to beat him this time. I'm trying to learn how to dodge XX attack."
I really hope some of that helps!
I usedto play test video games. I never would have approved ANY of those fights to be released. Its great if you got a lot of time and no life. but for the average player....no....they are horrible...like beyond horrible.
I feel like I just simply have to hard disagree with you, unfortunately. These fights were an absolute delight for me (but i can absolutely see how they are frustrating and challenging as well!)
These fights were marketed and designed
specifically to be hard because that is what people asked for. People complained endlessly that there weren't any "super hard make-me-cry style boss fights" in the base game. So the team said okay, that is exactly what we will put in. Challenging
optional fights. If Yozora was just part of the main base game, just a random story boss with no warning then yes, I would agree with you that having such a challenging fight compared to the rest of the game would have been ridiculous and anyone monitoring quality control should point that out. But...this isn't a random level that is just stupidly hard for no reason. It's a secret fight that is
supposed to destroy you, designed and marketed and
advertised to be hard, that absolutely your "average" gamer
should have difficulty in fighting. Like...that is the point.
I mean, you say you play-tested games but like...how would you have felt about play testing a game like dark souls? Would you have said it was awful and crap because the game is literally designed to expect you to die and die frequently?
I mean, your opinion is your opinion and I'm not wanting to stand here and tell you you can't not like something. If it's not your cup of tea then it's just not and that's okay. But to say this should never have passed any sort of quality control is a bit much, imo.
Theres a reason most games that do insane fights like that, have a easy version.
But...there actually is an "easy" version, though? They implemented an ENTIRE set of codes that you can mix and match to make the challenge appropriate to your skill level. Not only can you set the game on beginner, you can give yourself assistance all the way to making yourself straight up invincible, basically. While yes, you can absolutely just toggle on the 1-hit-KO just to see the cutscenes, you can also just opt for some of the "lesser" ones like regen hp, mp and auto block if you are having trouble guarding and still want to "do" the fights. Bam, a customizable easy mode.
Like...I really don't want to sound like I am insulting you or treating you like a child, but those codes are in the game for a reason. If you can't get past a fight for whatever reason the solution isn't to rage out the game and say it is horribly designed and crap because it is a challenge. Just take a deep breath, make a file that has the codes active and go to town.
I honestly don't understand why you are banging your head against the wall to the point that you are HATING the game instead of just...using the tools they put in the game to help you. If you don't have the free time to practice and you need a little help there is 100% no shame in using codes to help you. Life happens and if anyone makes fun of you or thinks less of you for it, that's their problem. Games are meant to be fun and if you aren't having fun then stop torturing yourself, just let the game give you whatever helping hand you think you need the most.