"Dr Menou, along with Dr Serge Tabachnik, created computer dynamical models of the known exoplanetary systems to see if it was possible for Earth-like worlds to exist for long periods in the so-called habitable zone."

That's what was done and that's the main part of the article you referenced. There is nothing really "new" here other than instead of speculation, these guys spent some time "studying it" and came up with some results which could be considered "unexpected".
This study did not prove that earthlike world were rarer than what was previously considered to be the case. It did not even address the systems yet to be detected once our resolution and time spent studying them improves [we don't have the resolution or spent the time needed to detect a system such as ours- say if there was a system "exactly" like Sol's which was about 20 lys from here].

There is also a host of other problems e.g. we don't "really" know that gas gaint typically migrate and gas gaints could form in short period of time, etc.