Okay, what? You are going to have to explain this.
DoA4 is one of the worst fighting games ever created. It is a functionally and mechanically broken game from nearly every single core that a fighting game can be.
I can understand not liking 5 as much as 2 or 3, even though I will disagree with you there, but I can not understand 5 not being a good as 4. Because's 5's mechanics aren't fucking busted.
Wait, what's so bad about 4? I know I'm not great at fighting games -- they're fun, but I'd lose against most decent players for sure -- but DoA4 seems fine. I've played it enough to get all the costumes and some beyond that, and it seems to be basically like 2, 3, or 2U, but with some improvements and better graphics. 2U is also amazing and might be the best overall game in the series, but counters maybe do a bit too much damage in that game, it's my one issue with it. In 4. counter damage feels just about right -- I think it's a bit less than 2U? In 5 counters do far too little damage, which is one of my major complaints about the game -- DoA without counters isn't DoA... and while 5 has counters, they are so weak that they don't always matter nearly as much as they should.
I'm a Lei Fang man myself, but I'm more annoyed with Momiji being included in the list. She's a guest character and doesn't belong there any more than Pai Chan or Sarah Bryant. At least Nyotengu is an original DoA character.
What? DoA characters appearing in Ninja Gaiden and vice versa aren't "guest characters", they're just characters from the other series that developer makes, which is set in the same world, appearing in this one. I don't think it makes any sense to call here a guest character, Ryu has always been a character in DoA after all so of course it makes sense to have the other characters in that series end up in DoA eventually.