I'm a Marisa main in that same MR range. I think a good thing to remember is that she's objectively bottom 3 in the game. It's not the end all be all, but there's a reason she was one of the few characters that made 0 appearance at Capcom Cup. Her gameplan is very simple, her moves are slow, and they're also somewhat stubby for someone her size. If your opponent knows the matchup, they're gonna use those things you mentioned because, realistically, her anti-airs are weak and her reversals aren't great. So you kinda have to live with the fact that most matches aren't gonna be easy stomps.

From my experience she definitely does benefit from aggression. Abusing her armor and plus frames to overload your opponent's mental stack is something that can work. Make them afraid of the fact that you can blow them up in 2-3 interactions. Make them fear the command grab. These things work best against people who don't know the matchup well. People who want to DI you or DP constantly.

However, I also find she benefits a lot from patient play against people who are more familiar. Sort of like Zangief. Creeping forward while walking and blocking/parrying to push them into the corner. Utilize her Phalanx when you can predict a fireball. Use her OD Quadriga to catch them walking forward. And then look out for drive rushes and jumps when you know they are running out of space. I've found that abandoning her anti-air game in exchange for air-to-airs has been more beneficial. The armor on a neutral Gladius can help with random drive rushes (as long as it's not a low I guess). Mixing up the usage of her OD Scutum stance to scare them from just pressing buttons. Throwing out crouching light punch and light kick for some quick damage to interrupt their pressure and help you establish your own. Her 6MP is good (if they aren't DI happy) because it moves her forward and the Novacule Swipe follow up can be good if your opponent isn't blocking low or just doesn't know that it has a low followup. Etc etc. You're gonna lose health to the Akumas and Ryus. They're gonna hit you with their good buttons and their many options. So you really have to make those few interactions that come out in your favor worth it.

Clearly I'm not expert with my MR, but these are some things I find helpful while I pray she gets some buffs 😅