On the other hand, you could make an argument that because D'Va is a gamer, she's probably played MGS before, and knows how to defeat Mantis. But D'Va doesn't really have the ability to warp reality to plug a theoretical controller into the second port.
It is actually possible to beat Mantis without switching Controller ports as Snake, but it takes a very, very long time, during which, you can easily make mistakes and take damage. Apart from her mech-self destruct (which would be a final gambit and takes time to charge anyway), D'Va really has no way to do anything more than minuscule damage to Mantis.
D.Va is not just a gamer, she's
the gamer.
Let's put aside the racist stereotype of Hana being South Korean, therefore she's amazing at game, and look at how Hana got in position of getting a Mech: she's in the Korean army. That's right, Hana didn't get bored with being a World champion gamer, but the presence of an omnic monstrosity called for the government to create MEKA's, and look towards Hana as being a pilot for the battalion. Whilst these two worlds will never collide outside of this tournament, but I'd say it'd be a fair assumption to say that this omnic monstrosity may well contain the same destructive powers as Psycho Mantis. I mean, this monstrosity levelled South Korea on multiple occasions, as well as its neighbours
(I'll post a link to her official lore story at the end, if you wish to confirm).
D.Va is also a global icon in the gaming world, and streams her real-life encounters for her fans to see. With D.Va being a World champion gamer, it isn't out of the realm of possibility that D.Va used multiple monitors, one which showed chat from the observers. The controller argument, and the difficulties in defeating Psycho Mantis without switching ports, could potentially be nullified by one of the many people watching her streams, even providing play-by-play call-outs on the array of moves Psycho Mantis has to offer. Furthermore, I'd champion to say Hana Song would have multiple options at the ready should Mantis have any tricks up his sleeve, readying up many ports and controllers in her Mech for all occasions. Admittedly, these arguments are stretching the limits; however, Mantis being able to pull some controller shenanigans in a "real-life" battle also seems a little on the stretchy side.
Being a champion gamer, she's dealt with a multitude of mental tactics employed against her. Hackers, cheaters, DDoS attacks... you name it, D.Va has probably encountered it, especially at her level of competition. Again, this is being stereotypical/racist, but there are a ton of gaming hackers in South Korea. On top of this, she's competed amongst the best legitimate players in the world, all of whom are high-skilled gamers; what does Mantis have in his arsenal to topple a high-skilled gamer? Moreover, what can Mantis really do against someone who has experienced the type of hacking and mindfuckery that Mantis was remembered for?
Oh... and did I mention that D.Va was recently buffed?
---------------------------------------
I'm going hard in the paint for D.Va, but ultimately, this match comes down to how quickly Mantis can employ his skills, and take out D.Va, before she gets closer, and/or becomes fully charged and let's her self-destruct blow him to kingdom come. D.Va, being the world champion gamer, shouldn't take her too long to figure out a gaming opponent such as Mantis, figure out how to expose his weakness, and call for the towel to be thrown in.
As I said: D.Va is not
a gamer, she's
the gamer. Psycho Mantis was not
the MGS boss, but
a MGS boss.
The gamer should be able to beat
a boss.
D.Va outplays Mantis, and takes the victory with a self-destruct.
---------------------------------------
Source: https://playoverwatch.com/en-us/heroes/dva/