I'm unsure of whether Peach really needs a secondary or not, but it's always something in the back of my head. I've considered Peach and Dark Pit a dual main for a long time, but anymore I'm not seeing as much need for him. He went from my main, to dual main with Peach, to secondary, to maybe even rethinking him even being there. I'm not doing tournaments as of now though, and those matchups I think are bad will be a lot worse with a smart player. He's really not as solid as my Peach though, and he's also really not that much better than my Greninja, Ike, Villager, Diddy or a couple other friendlies characters I could decently easily train up for that position. I'm not counting him out at all, he's probably still the best character out of those, but I'm much more open to a switch. If you have an opinion on which of those best compliments Peach or if you feel Peach doesn't need a secondary, I welcome any educated opinions.
*EXTRA* - If you're bored and have the time, here's the reverse tl;dr. A run-through of my smash character history (mostly anecdotal, but might give you some insight idk):
I had no idea about the competitive community for smash before the hype for smash4, so my experience with Melee and Brawl was casual I mean I was 7 and 14 on their releases, so yeah. We got each console a little late cuz we don't have a lot of money, so I was actually playing them starting at like 9~ and 15~. I played with my siblings and friends with items on. I played Sheik and Fox in melee, and Zelda in brawl. Me and my brother were a good bit better than every other player around us by brawl but were still just casuals who only played multiplayer, we were just better at shielding, grabbing, actually using the whole moveset, etc. Not much else to say for those eras.
When the hype for smash4 came in, my brother was doing a ton of research into it cuz he was super excited for it, which accidentally lead to us both getting into watching competitive Melee matches in addition to info for the new game. I had no interest in getting a 3DS because I knew that would never last for me once I could use an actual controller, but I would play a couple matches vs CPUs on my brother's 3DS when I'd hang at his apartment and while my family met up for a vacation. During that time I was pretty much only playing Greninja. I've never played characters for what games they were from (haven't played Pokemon since Gold), I just loved his moveset. He seemed like the character you could get the most creative with, and was super unique and all pretty new for the series. The WiiU version came out, and I was still playing him. I gave almost everyone a couple chances every now and then, I kinda liked Dark Pit, but Greninja seemed like who I was going to solo main to the end.
Then a couple months into the game we were chilling and playing and that night I was on a kick of giving other characters a chance again. I realized I hadn't actually given Peach a chance ever in any of the games. Even that night it was kinda jokingly. I'm perfectly secure in my manhood to do somewhat girly things, but there was just always something kinda weird about picking her (I've still never seen anyone pick her irl in all the years I've played smash). Probably just people's expectation. Played her one time and fell in love instantly. I wasn't even playing her well at all and won my first game with her, and the people I was playing with noticed the immediate connection, even if it was faint. I was a Greninja and Peach main for a few more months until I hadn't progressed much and thought Dark Pit had more competitive viability. Lets keep in mind this is my first game I have ideas about competitive play for, and Nairo has shown good results with Dark Pit at this point while my subpar skill mixed with seeing no players for them leads me to believe Peach and Greninja can't be very good. Sure there's Amsa and Umeki at this point, but I didn't know anything past the US. I've never fully dropped a character, they just became what were going to be casual characters in my mind, and I played them very little and stopped trying to improve them.
Since I had moved on from both my mains and was used to thinking about the game competitively with a support character in mind, I decided my secondary would be Villager, since he was one of my better casual characters at the time. There was a brief time around then I considered Diddy too, because he felt pretty natural and he was just obviously good, but I never really did anything with him. This phase lasted another month or two until I missed playing Peach and Greninja and brought them back. At that time I realized it was going to be hard to ever fully leave any of my 3 first characters, Peach, Dark Pit and Greninja. I might eventually decide to commit to one or two for competitive, but they are all my characters for sure.
After a while Dark Pit pulled ahead of Greninja and I've been dual maining Peach and D Pit for like half the game's life. I've finally been at a point where I do a lot of research, note-taking, labbing and actually really getting good with Peach and at the game in general, which now leads to my dilemma with Dark Pit. He just doesn't have very much potential (he's just solid), and I'm not sure that I need him either. I feel like if I do one last switch, it's most likely going to lead to me bringing back Greninja, because I think deep down I've always wanted it to be Peach and Greninja, IMO two of the most unique, complex, and creative characters in the game. I'm still totally open to any of the other ones though. It's just that I need to commit, because I lost a lot of time that I could have been labbing Peach and Greninja back when they were my dual main, rather than all of these character choice decisions based off of feelings and insecurities at the time. At least now that I'm better and understand why I want to play certain characters, I know one thing for sure: I'm 100% sure Peach is my true main. I can get lost not knowing if I'm going to have a secondary or who it will be, but I know that she isn't going anywhere.