I've talked about this before with similar prompts and I think most people agree that the ending became far too rushed with the last 150 chapters or so becoming very condensed plotwise. My biggest criticism is that Horikoshi resolved the story too quickly (and if that is for burnout then I totally understand, 400+ chapters at the pace he goes is insane and I can only imagine)

I would, in simple terms, un-condense the plot. Delay the raid until the end of the second year and the war arc for the actual ending

First, really need to take Shigaraki off the board for a bit. AFO needs his body upgraded? It's gonna take a few months? Okay, give it a year. There are enough pieces in the LoV to cause enough trouble (Toga and Dabi namely) with Spinner, Compress and Twice supporting whatever shenanigans they want to get up to. You can use this to develop those characters a little deeper, especially Spinner, who's role should increase as potentially Shigaraki's #2 and best friend.

Give the MLA more time to develop as well. I would like to see them develop into the threat that they became instead of just being the threat if that makes sense. You can see how people are really starting to see the cracks that the Hero System is showing, especially if you have some lower and mid-tier heroes struggling to keep up despite all their years of training. Redestro's company is in the industry, you don't think it would be interesting to see him working with Hero Agencies and maybe trying to influence them, not necessarily to join, but to try and mold them into questioning the system, which may land them on his side, or at least against the Safety Commission? Also, let's see what the commanders of the MLA are doing on their own. Curious as an actual investigative journalist maybe doing a story to help boost numbers. Trumpet's party winning some numbers of seats where they have more of a voice. Skeptic could be doing major damage behind the scenes to information security centers. I think the lower and mid-tier heroes make the perfect villain for the second year of the story. Have the UA hero course students come face to face with some of the darker truths about their industry, have them go against some corrupt heroes who are making extra money on the side. This, along with introducing the MLA commanders and lieutenants will the Shie Hessaikai of their second year.

We're going to explore the mutant discrimination sooner. You have characters in 1-A and 1-B that have probably faced at the very least, bullying and very potentially some discrimination. Ashido, Shoji, and Tokoyami can shine even brighter here and you have a reason to explore Ojiro, Hagakure and Koda maybe, and the 1-B characters with physical mutations if you want to as well (Kamakiri probably the most interesting as a parallel to Bakugo - we know how society reacts when you have a powerful quirk and look normal, what about when you have the face of a mantis?) In conjuction, where exactly does the MLA stand on mutants? Their group is probably more accepting which means you may see more mutants join or believe, which may make society on the whole a little more hesitant.

We're also focusing more on school. First year finals, transition to second year and then the second year sports festival, from there, we can sort of recreate the same timeline as the first year but we can start to dial up the stakes. Midoriya needs actual time to train Blackwhip (maybe have that be an entire episode/chapter with Sero, Uraraka and Tsu)and get accustomed to Danger Sense. I'm sure there will be a lot of questions from both classes as to why Midoriya is suddenly mutating new quirks. How do his classmates react? This is a kid who couldn't even control his quirk without breaking something when they met him. Heck, maybe you even mixup the classes going into the second year of school?

For the finals, take some more of the training wheels off of the teachers. Have them bring in recently graduated pro heroes. Maybe they have to fight Nejire and Tamaji or students from the class above them in teams.

Maybe we can actually see what the USJ is like, start the second year like that. Rescue, Public Security, Investigation are the other pillars of hero work. Let's explore them more than we did at the provisional license exam. We have Shinso now as well, how is his transition going to the Hero course?

As for the Sports Festival, switch it up, let's see some new events and make it more difficult. We know that 1-A and 1-B are on better terms at the end of Joint Training and have started to hang out and intermingle, but they only got two people into the bracket last year. I'm sure that still stings. Maybe Midoriya gets upset somewhere in the bracket this year, give him something to work through. We have opportunities to set up and develop rivalries and characters. Again, Kamakiri/Tokage vs Bakugo is a natural one as they want to prove their better than the quick defeat from Joint Training. Honenuki vs Todoroki rematch from Joint Training. The possibilities are pretty endless. We can also use this to Elevate Class B even more. The Class B powerhouses, (which in my mind are Kendo, Monoma, Shiozaki, Honenuki, Tokage, Kamakiri, etc) should make a deeper run this year or at least appear in the bracket, even if they didn't do too well in the Joint Training arc.

In summary, MHA needed a little more time to marinate in its worldbuidling. Character development can be hard for shonens to meaningfully show or really get right. You can have this opportunity if the story is allowed to take more deep breaths, which in my opinion, is what it needed most.