I feel like the question here really is "do they need splitting?" Because more than two stories that need filling out, you might actually have one story that needs pruning down a bit.
There are plenty of High Fantasy stories that contain sentai like elements, like Magic Knight Rayearth for example, so there's really nothing stopping you combining them. Realistically, you'll probably need to make the comics you want to make one at a time anyway even if you do split them, or at least have one as the "main" story and one as a potential spinoff, so I'd recommend limiting yourself down to one really good comic idea first that if that was the only comic you were making for a while, you'd feel happy.
Making a long, drawn out Japanese style shounen manga, complete with filler arcs simply isn't realistic, never mind two of them. Assuming you're planning this as a webcomic, you need to remember that shounen manga releases at a pace of about 20 pages a week. You know how many pages a week I can make of my shounen-inspired comic at a decent level of quality (and in colour, because black and white is a really hard sell in webcomics) while working part time to pay my bills? TWO. And even if we assume that at some point you might make money from this venture and it could become your job... you need to get to that level of popularity first, which could easily take at least months, if not years.
All this stuff about arcs and genres is a distraction. You need to focus on just planning out a story about a protagonist who gets into some kind of tricky situation and works towards a goal, and in doing so is changed by the experience and grows as a person. Then you can think about how elements inspired by shounen manga can help support that. Whether it's the story of one person who starts in a disadvantaged position and must overcome increasing threats through building their own personal power, in which case, it's a battle manga, OR if it's about a protagonist who must learn to be part of a team or a leader, or a group of dysfunctional people who must learn to be a strong team, in which case, it's going to feel more sentai.
Pick the one story that has the most compelling protagonist and overarching story, and make JUST THAT ONE. Take any elements that fit into it and make ONE really great comic that's fun to read and emotionally satisfying. If it's amazingly successful, you can make a spinoff, and you can worry about what story elements and genre or whatever will go in that if and when you ever make it, but right now, it's a distraction. Forget about it! Don't jeopardise actually managing to get the IP started by dreaming about some expanded universe you might not ever get to make!
Stop thinking about your comic as some grand big IP and for now think about it as ONE PRODUCT. The DC Cinematic Universe never really took off specifically because they were thinking so hard about making a cinematic universe, it distracted them from the importance of making one really good movie that works on its own and sets up one really engaging character people want to see more of to kick it off. You need to make Iron Man before you can make The Avengers. One really solid standalone movie, or in this case, comic.
Make ONE GOOD COMIC. Don't think about spinoffs or multiple works in the same setting. You don't know yet what elements of the world readers will like, and you don't know who the breakout character/s will be, so you can't know who or what the audience will want to see more of! The things you need to be preoccupied with are not "What genre of Japanese manga is this?" (because on Tapas and Webtoon, the answer is literally going to be "It's Action" or "It's Fantasy"), or "How can I make these two works fit into my extended universe?". The things you need to focus on are:
"How can I make this one comic appealing to modern webcomics platforms and build an audience while keeping elements I like?"
and
"How can I tell the most engaging story possible with this concept that will really capture peoples' imaginations?"
Focus on that. Make one good comic. Just ONE. Pick one character as the protagonist with a solid story arc, include a small supporting cast to help facilitate it. Use elements from the genres you like and that fit with the story you're telling, and always think about the audience's enjoyment first. Think about how you can entertain people, because this entire big plan you have about a setting and spinoffs will live or die on your ability to tell one great story that makes people fall in love with it. Remember: There's a reason Star Wars got sequels and spinoffs but Jupiter Ascending didn't; Jupiter Ascending has a really great setting... but it's a bad movie, and nobody wanted more of it because of that.
