Greece 2 week itinerary

I’d say that’s a reasonable plan, though you could stay in one (either) place and accomplish the same thing.
Given transport logistics you may not get a full week in both places so take that into account.
I feel like the Peloponnese has the edge in terms of cultural/historical attractions but it has plenty of nature areas to explore as well.

I would say you could get that balanced itinerary with two weeks in either location. They both have nature, beaches, wineries, olive oil factories, historical sites, and ruins.

I have been to both but not in the same trip.

Both are worthy of a trip.

Crete is the largest of the Greek Islands and would take weeks to explore.

The Peloponnese is a even larger and would take even more time to explore.

One week on both would be fine.

The only issue is getting from one to the other.

You can get to/from Crete/Peloponnese by ferry but it's limited but would be the least expensive and least time consuming.

The are ferries in Neapoli and Gythio in the Peloponnese to/from Crete so you would have to make arrangements that way.

If you have a car you'll need to make sure the car company allows that.

On the other hand 2 weeks in the Peloponnese or Crete would give you enough time to explore either location without the worry of how to get to/from either location.

I go more for historical sites as well as scenic places.
https://www.tripadvisor.com/Attractions-g189413-Activities-Crete.html

https://jaywaytravel.com/itineraries/ultimate-peloponnese-2-week-private-tour

I am with tommy's thoughts, just choose one destination or the other but not both. Both are great choices but each are so large you need a month to really explore just one of them.
When changing destinations in Greece, you pretty much us up a whole day just making the transfer so choosing one of these destinations essentially gives you an extra day.
If I had to choose I would concentrate on Crete.

DH and I did a two week trip in 2018 that was roughly split between Crete and Peloponnese. We still talk about that trip fondly. Here is our trip report in case that's helpful: https://community.ricksteves.com/travel-forum/trip-reports/two-week-trip-to-crete-and-greek-mainland. To change our trip to shift more time toward the Peloponnese I would replace Paleohora and Elafonisi with mainland time. They were the least Wow for us. Admittedly we're not huge beach people. Our Day 12 kayak trip near Nafplio, although we loved it, could also be replaced. That would free up around 3 days on the mainland for perhaps Monemvasia+Mani penninsula areas, or Delphi + Meteora areas.