Why are they unrealistic? Because the proposed bands are too big (according to you)?
There are many artists who take the most successful bands as support. Amon Amarth is currently touring with Carcass, Orbituary and Cattle Decapitation. Slipknot took Behemoth as support in 2020. Metallica is touring much of the world next year with major bands like Volbeat, Pantera and FFDP. And Maiden took bands like Ghost, Killswitch Engage, Alice Cooper, Shinedown and many more as support in the past. Just because a band has some success doesn't mean they can't be support bands.....
Maiden taking Raven Age on tour is a clear example of nepotism and there's no other explanation for it. There are so many bands that would be so damn proud to be the support act on a Maiden tour. I believe Scott Ian (the guy from Anthrax) even said it in an interview a while ago. He hates being a support act for another band, but for Iron Maiden he would love to go on any tour with them. And believe me when I say there are many more bands who feel the same way!