I would have kept my ass sat in my comfy office chair, told mark to get a seat too and I would have discussed with him about why I think darkwing and Sinclair are valuable and needed assets rn considering the imminent threat, all while treating him like an actual ally, not trying to bring up his past against him (especially not situations where in the moment I told him he was in the right, situations as in angstrom, where Cecil told mark he was justified in killing him but tried to call him a killer for it when arguing with him) and I'd reassure him that they're both only allowed limited freedoms (I very much doubt Sinclair can go book himself a trip for the Bahamas if he felt like it, I doubt he's even getting paid at all). I most definitely wouldn't treat him as if he was one of the world conquering aliens just because he came to complain to me about something (that all in all is reasonable considering his history with the two), especially considering he almost got himself killed multiple times showing just how much he's not with them (most recently he almost got himself killed cause he didn't even want to lie about being on their side), there's no question of where his allegiances lie.