@accuracy powers/stunts;
If you are worried about the numbers side of things, here are some things you can do;
1) In order to have accuracy or dodge powers, request the character's concept include skill of some sort. A brute like Magog for example has no accuracy boosters despite being a primary melee denarian.
2) Impose some sort of soft cap. I.e. request your players that their attack skill modifiers be no higher than skill+3, the same level supernatural speed + stunts can bring them. If you are in a high refresh game, that would be skill+4, the same level mythic speed + stunts can bring them. This would be for static bonuses though, not abilities that cost FP or stress. (those need to be on par with magic so no cap)
3) Accept no new accuracy powers. When players suggest a new attack boosting power or stunt, it will be considered a reflavor of an existing power and not stack with it. That way, you only ever need to worry about the accuracy boosters already in the book.
@magic:
Yeah, it can get really powerful really fast. At submerged, a weapon 10 control 11 caster is doable without any powers offering rebate (IoPs, Dependency, Human Form). At twice submerged refresh, you are looking at weapon 17 control 19 for really strong warlocks. That does not so much create an imbalance between casters and other character types as make any combat that involves a caster a game of ICBM tag; who goes first nukes and wins. That is why I usually set aside about 1/4 of the refresh of any casters I play to get non-blasting stuff.
As for foci, some foci are easily broken. But others are much less so. If instead of a wooden rod you make a tungsten bracelet, hide the bracelet under your sleeve, wear several identical bracelets (1 focus and 3-4 fake foci) and conceal each bracelet under its own veil, it is considerably more difficult to get your foci removed. Of course, if a strong opponent is close enough to attempt to break your foci, they are also close enough to attempt to break you.