Using the large landing legs is not a problem, to me it's fine.
Here is my version of the challenge:
The proof that I comply with the rules:
First step, reaching orbit:
Then reentry. By first killing my horizontal velocity, then opening the solar panels:
Once the ship is slow enough to avoid burning, the panels act as huge aerobrakes. If you do this, you just have to make sure you place them on the top part of the ship to keep it stable: