I'm going to try to spell out why I think Bodyguard is a better choice than Loremaster-At-Large, given how similar they are in many respects:
• The Empire needs a troubleshooter more than the Dwarves do. To use a mining metaphor, the Empire still has many rich seams of problems for us to mine through, while the Karaz Ankor is a lot more tapped out. The Empire has a great deal of immediately active problems for us to work through, and trying to bring some unity back to said empire is an excellent cause.
I am going to focus on this one, because I think I finally nailed down what exactly bother me about Heidi option - or rather, what you and some others
think it is - so much.
(well, with very much real aside of "Empire has myriad of Wizards and several more Grey Lord Magisters, so marginal utility of Mathilde there is way lower than in KaK where she is without an exaggeration unique, which makes the whole rationale a bit wrong, IMO)
To start with, if the option was bland Imperial Spymaster and not Heidi's right hand election rigging woman, I'd be quite a bit more tempted by it.
As is, thing about Heidi is, she explicitly stated, more than once, that for her priority one is her son getting power. Even if it means Child Emperor, even if it means more competent and suited emperor being sidelined in favour of a kid just because of political shenanigans. Does this really sound like "Imperial troubleshooter" to you?
Mathilde
will indeed do Imperial troubleshooter, only inasmuch as it benefits Heidi's goals. And if some Imperial trouble, say, has possibility of, say, making a competing candidate for the Throne busy for the duration of election and unable to campaign in full - what do you think Heidi would prefer, this trouble being solved or it going on to increase odds of Mandred winning? She will not go as far as to create such trouble, I presume, she's not outright malevolent (and it would be risky), but she
does explicitly put good of Mandred above good of Empire.
And that's the gist of my problem with how you present it: you present the position as Imperial troubleshooter, but it is not. Any imperial troubleshooting will be coincidental to the goals of Heidi, and not the actual goal. It is
not position of Imperial troubleshooter, it is a position of
Heidi's troubleshooter. Good of Empire may come as a result of it, but it will be a side effect of electoral politics.
And yes, it
would put Mathilde in a position where she can, in theory, contest Heidi's ambition if she wants to. But, Heidi is one of few people who are probably better than Mathy at Intrigue, and it'd be playing silly buggers with Heidi on her home turf of court politics. And we cannot really trust Ranald to have
our back on this one either. So, odds are, Heidi's agenda will be, within margin of deviation, actual Mathilde's agenda too.
edit: tl;dr: Empire needs
a troubleshooter, but a) it has plenty of Greys and some are Lord Magisters, while Dawi have zero; and b) position is not Imperial but
Heidi's troubleshooter.