You got excellent turnip game, love how you pretty much always have one. A mistake you made a lot is that you rolled far too often. I would say defiantly work on using rolls very very rarely. Rolls are super situational moves. You should practice spot dodging but that as well is super situational and depends on your skill of reading your opponent. When you're up against experienced players you get punished very easily for rolling. Experienced players look at for this kind of stuff. Wave dash to space yourself. Rolling is not a good option for spacing. With a wave dash you can grab, attack, run, and jump out of. You have options with wave dashing. With a roll there's always a lag afterwords where you cannot do anything. This makes rolls super punishable and very unsafe to do.
At 8:16 and around 8:25 in the first video you missed perfect edge-guarding opportunities and just sorta stood there. I don't know if it was a bait, it didn't seem like it, but you could use some work on edge-guarding too. Peach's dair is super good for edge-guarding characters without high priority up b's, like Fox, Falco, C. Falcon, and Marth.
Also you should defiantly follow up for combos out of grabs more often. Instead of getting a turnip why not jump up for a bair or nair? Or if you really got some good reads or spacing on your opponent go for a fair after the grab. I noticed you down grabbed and just sorta stood there. I don't know if you were baiting an attack but you could have defiantly did a forward tilt or dash attack. I noticed you did this often. So I would say you should totally work on follow ups out of grabs. This really showed in the second video near the start. You side tilted Samus and didn't do anything, and then proceeded to down grab Samus and not do anything as well. Peach's aerial followups are great, with enough practice you can easily rack up 70+ damage and your opponent cant do anything. It's even easier to do these followups on stages with platforms.
In the first match in the second video you were on Fountain of Dreams which is such a good stage for Peach due to her dsmash. Platforms are Peach's friend use them to your advantage with combos, followups and your dsmash. Peach's dsmash is very dangerous, use it as much as you can to pressure your opponent and rack up points. How low the platforms get in FoD really help her dsmash because you can easily get into the sweetspot for it and rack up 50+ damage. Peach is very threatening to non-sword fighters on stages with platforms because of her dsmash. If you're winning don't approach, let them approach you, stand on the platform and just dsmash. It may sound cheap but it works
Another good thing about Peach is how you can easily pressure with her bair. Bair is so good for spacing and pressure. In the second video I noticed you had issues with pressuring. A good pressure combo for Peach is float>dair>nair. In the second set I saw you dair >float cancel>dsmash which was really good. Work on doing stuff like that more often
Also don't float right after being launched. If a player reads that you're going to do that they can easily punish you (especially C. Falcon players)
Also work on reading and finding patterns that players do to punish them. I noticed the Falco you went up against was very repetitive with his moves. You're excellent at shield grabbing and knowing when to shield. Although you do it too often so players will know that that's what you're going to do. Which means there wont go near you with your shield and either poke it or if a character has a ranged grab they'll grab you.
Things you're good at:
Turnips
Grabs
Shield Grabbing
Things to work on:
Follow Ups
Not rolling
Edge Guarding
Pressure
Spacing
There is a Peach matchup thread, it isn't complete but it's super useful and full or good info. It's also got a Samus matchup as well. The title of it it "VaNz Stuff.. about Peach (Tactical Discussion)" I can't post a link to it because I don't have enough messages but it is on smashboards.