The Gouketsu Summoner losing to a notoriously lazy non-combat specialist would look very bad for us.
Why do people think this? Do you even believe it yourself or is this just an argument you want to make to Jiraiya?
Because Shikamaru is definitely not weak nor lazy - where it counts.
Being known as the lazy guy out of combat is a very useful reputation to have, especially since you can now take this assumption people have of you and play it off in combat situations. And you'll likely fool some people into believing it and underestimating you, case in point: canon Kakashi.
Once he is in a combat situation, Shikamaru is actually quite scary with his bloodline because not only is it a one-hit KO in many cases but it also lets you manipulate the environment (imagine having extra shadowy hands).
He also appears to have a decent Deceit score, likely higher than Keiko's, as implied by how he was playing off the whole Wood Release bit. He may have addressed the Kages while speaking but let's not kid ourselves that the show was for Ikeda's sake only. (And sure, all those gullible people in the audience who fell for it and now think the Nara are even more powerful than they really are.)
In addition, Shikamaru not being a combat specialist is only partially correct. Whenever someone is fighting Ino, Shikamaru or Choji 1vs1 in the arena, they are basically fighting 1vs2 (or 1vs3 in Choji's case) because their specializations are well suited to helping each other outside of the arena ground.
Ino provides the insight on the opponent's psyche to enable social attacks and helps Shikamaru refine which types of plans will or will not work (e.g. don't try to intimidate Keiko, rile up Kiba and abuse the fact that he is the type to attack head on, etc.). I can't think of something Choji offers here but it's possible he provides them their blend of soldier pills which they could take before (or during if they want to risk it) the match.
In theory, a Shikamaru supplemented by Ino's report could knock out Keiko likely before the match even started. I don't think he will due to
CONSEQUENCES but it is another reminder that we are not fighting a 1vs1 battle.
(Unfortunately, our way of support is non-standard seals and Noburi's chakra water - all of are banned under the tournament rulings which leaves only Hazou to help plan with Keiko.)
First thing that should have been done is asking Keiko's summons for intel on ISC techniques to - at the very least - get an aspect bonus against them. It'd be silly for Keiko to get surprised by abilities she should have already known about just because she forgot to debrief her summons.
