How often are you drawing Blightsteel in your hand and realizing Tinker is almost useless at that point? With no way to discard it and only Brainstorm to put it back or Ponder to try to shuffle it away before you draw it, it seems like a liability at times.
in an opening hand that can't do anything about it happens maybe 1/10 games. drawing it randomly on a turn so its in my hand maybe 1 in 6 or 7. i feel like that happens about 1 in 3 rounds. but i have many ways to discard it, all of the draw 7s, the LED the brainstorm, discarding it because necro overdraws it stil gets shuffled in because its replacement not trigger and on occasion i have therapy'd myself to put it back.so i rarely find it to actually be "dead" in my hand. every now and then i get to cast it for a trillion mana or off my minds desire but those are weird statistically anomalys. the number of games where i could not tinker my robot into play and i lost because of it is actual 0. it has not yet cost me a game. there have been 2 games wher ei had to tinker for jar because robot was in hand but i won those games anyway. results oriented this is only a sample size of about 50 games or so in comp REL.
and yes it is very hard to find room for the tinker package. everytime i look at my list im always at 61 cards and cut 1 thing almost at random between chain of vapor, cabal rit, and other nonsence. so i completely understand not being able to squeeze them in.
sadistic sacrament? the 3 mana exile 3 cards from your opponents library? i guess that would work against any not me storm player as a win con. kind glad i play 4 wincons.
maybe im just really biased because of danny but i really just like having some elephants go around smashing all the artifacts in play more than trying to out mana the cost or play through with some rodents. that does require a 2nd mountain tho so i guess thats not a plan you can implement.
oh about the 12 lands thing. while i do run 1 less land than the norm i am playing 6 duals and the academy so i end up having more actual lands overall compared to 3 duals 2 basics and academy. i tried playing basics but island kept not being able to cast things and getting swamp felt weird when i wanted to cast 3ish blue spells in a turn. i actually fetch volcanic island more than badlands. also playing at least 1 of each of the duals let me have perfect mana no matter which grixis mox i draw.
im curious what kind of hands you keep though. you said when you mullagin for fast hands you tend to. when i say go off i dont nessacery mean you win every game on t1/2. i mean you cast a must counter spell at least once a turn. so a turn 1 necro counts as going off even tho you didnt win the game. a turn 2 tinker for a robot counts as going off even tho it might get swords. games go to several turns sometimes but that happens because my opponent had good interaction with me not because i always mull to something like triple dark rit lotus will dt. i also consider draw 7's with 3 fast mana sources strong enough to just play on turn 1. im not above going land mox sol ring wheel pass the turn.