I've never heard of them, and looking at wikipedia none of their movies really sem to have prepared them for the MCU. But, marvel tends to do a good job with directors with one or two exceptions, so they'll probably be decent at the very least.
Most of their directors have never had much, if any, big-scale tentpole work prior to working with the MCU:
Scott Derrickson - small budget horror films
Kenneth Branagh - mostly Shakespeare/Period Dramas
Jon Favreau - some larger scale work on
Zathura, but nothing else
Anthony & Joe Russo - mostly just TV work before
The Winter Soldier
Peyton Reed - Rom Coms and Comedy Dramas
Shane Black - small noir comedy
James Gunn - no-budget SF/F fair.
Only Joe Johnston had any true, significant back-history with large scale projects (Jumanji, Jurassic Park 3)
The big thing that separates those larger films from what they have worked on before is the Production scale, which in the case of the MCU is not only massive, but with a massive crew behind it also. MCU have a highly oiled machine working behind all of the directors, so I guess what they look for isn't necessarily "experience" but rather a personality and goal-structure that fits with the title they are producing.
You can see when that fails, where the two visions don't meet - Favreau on
IM2, Taylor with
Thor 2, somewhat with Whedon and
Avengers 2. But most of the time, the sensibilities, personalities and goals of the directors match the needs ans style of the film that the MCU want made.
I've loved all three films of these directors. Yes they are low key, but they are all visually and emotionally very distinct from each other, showing a good range. I have no idea what their pitch for
Captain Marvel was but, clearly it was either very in line with what Kevin Feige wanted, or was so fresh he was happy to throw away the pan and start with new ingredients. Either way sounds fine to me, because, at their worst his team have produced passable entertainment and at their best, they left me thoroughly entertained.
By picking the likes of James Gunn, Taika Waititi and now this pair shows (to me at least) that Feige wants these upcoming films to have as much unique personality and character as possible. I hope they all are able to add their best sensibilities into
GotG2, T:R and
Captain Marvel and given some freedom to explore what can be done
inside a monolith like these event flicks. I don't expect anything profound in the journey (Fiege controls the map here) but some nice detours to go along with the 'splosions, banter and green screen.
Hugo - encourages everyone watch
Mississippi Grind. Great road movie.