ok, so a platoon commander without portfolio doesn't much shift the needle for you as catachan, BUT a master of ordinance synergizes your artillery well at mid to long range. (reroll 1's) for the exact same price, also gets one sunday punch where he points and arty fires in from nowheere.
The vigilis detachment does not synergize at all with anything except basilisk or wyvern cannon, by which I mean if you have only earthshaker carriages, you shouldn't bother with it, as you will be unable to buff them with buffs specific for named units from the detachment.
The thinky 32 with a couple artillery pieces is a decent board control and support backup, and raining down
ap-3 shots is also always nice. I personally would against catachan in this instance because. (but to be clear, I ... I very much approve the two pskers you got out of your 46+15 points.)
Why cadia and not catchia?
1. your +1 strength isn't going to be much use without a priest or straken or melee weapons or more gaurd squads.
2. your reroll of shots is rerolling the lowest of TWO die on each earthbreaker, meaning you already have much of the functionality of the reroll. How often do you get double 1s? Is that worth giving up rerolls of ones (cadia) below? I don't know about you but I roll a LOT of ones when shooting.
3. cadians get 2 above, AND THE ARTIFACT "relic of lost cadia" which converts the guns to reroll all to hit and to wound against chaos for a round. Very powerful in the opening salvo, if synergized iwth a doublefiring wyvern or basilisk from vigilis. It even gives the 3 gaurd squads a prayer of damaging t4 or t5 units.
4. consider finding a way to take an inquisitor. They are awesome, at 55 points, you can (for example) throw an extra smite and castiogate each round, and its a decent if light coutnercharge unit.