The problem is, Lions naturally have amazing stamina. They can keep going after being impaled and such for a long time- continuing to go on is exactly something a Lion could do, and note how he died anyways. In addition, a Lion is also naturally stronger and larger than Hyenas, only kept in check by numbers of their pack.
Let’s also not forget that Scar would consider Mufasa powerful, as Mufasa’s the older Brother, and outright stated to be in better physical state. Him ruling the Pride Lands isn’t a power statement either, as he was just a great leader. Let’s not forget that, while Scar was able to tussle with Simba, Simba spent the majority of his life eating only Bugs- and improper diet for the Lion, likely leading to malnourishment if an actual Lion was used. We also see Simba get owned by Lioness’ in Combat plenty of times, both when his Girlfriend comes for him and is able to take down more hyenas than him, something a Natural Lion wouldn’t have.
Meanwhile, on the Real Lion side, we have a prime condition Male Lion. Standing in at healthy weights and prime physical age, this thing can do what Mufasa could do, better. It also has enough Stamina to withstand being smacked around by and impaled by Wildebeest and continue fighting on. This one has lived its life properly, and I believe it’s assumed it’s well fed as well. The only difference between Mufasa and the Real Lion, besides Intelligence, is Age- and since every Stat on Mufasas page comes from the assumption he’s no different from a normal Lion, the Younger Lion naturally should be able to take down a very Old Lion.
