So I'm a big Wally fan so I'm absolutely biased in this topic, but there is one stone cold fact that separates Linda from Iris or Lois.
Iris and Lois were created to be love interests that fawn over the Superhero whose franchise they're in. Things change and retcon over the years, but that is definitely what they were created to be.
Linda was created to be her own character. As a matter of fact, she was originally created to be antagonistic towards Wally because, at the time, Wally was a showoffy, big headed young man with superpowers and acted like one. Wally was in a different relationship with no particular plans to match up Wally and Linda when WML created Linda. Their relationship came about from the growth of their relationship from antagonistic, to peers, to friends, to love interests, to marriage, to family. And that natural growth, that is so characteristic of Wally's entire time as The Flash, was something that was constant through their history until they got rid of them.
Lois has gotten more screentime and, frankly, more individual development due to sheer volume but her character history is a thousand times more inconsistent than Linda's because of it.
I just take issue with the idea that Linda is a Lois imitation when she was actually an original character.
And, on a more minor note, Linda's relationship to Wally is tied into his powers. If Lois disappeared Superman doesn't stop being Superman. And the lightning rod concept was obviously something Barry and Iris took from Wally and Linda, not vice versa. Superman isn't any less Superman without Lois and that story has been told a dozen times (though sometimes you get your Injustice style elseworlds that crap on Superman's character via Lois death). But it's demonstrable fact that Wally couldn't be Wally without Linda. His powers wouldn't work right and what we find core about him as a character dissolves pretty quickly without her. The Waid era, Wally's defining era, was kicked off with them starting a relationship after all.
To some degree, Waid's absolute love of Superman and obviously Lois probably leaned him, subconsciously or consciously, to making the female reporter Wally's love interest. So in that very vague, several degrees removed way Linda is a Lois derivative. But I think it's clearly different enough in that way.
Hell, think about it this way. It took...70 years for Lois and Clark to have a kid (I'm talking about Chris, btw, not Jon. If you don't think Chris counts then add 10 years). Wally and Linda were in a relationship from 92 onwards and their relationship fully developed to that stage by 2005 -- 13 years. And it wasn't some breakneck rush, their relationship was the core of the book nearly that entire time and was certainly a better developed relationship in that era than Clark and Lois. And that's a testament to how well they fit together, that they never really split up for an entire period to do weird rompy stories (hello Byrne) because people can easily imagine a Lois-less Superman. I can't imagine a Linda-less Wally any more and the second they brought Wally back the first thing he does is think about Linda. When Superman ate the New 52 retcon bullet they were shipping him with Wonder Woman.