u can keep playing the heroes u specialize in to climb better.
if u are good in BB, then keep spam BB, there is no match where BB is not a threat. its an universal tank and lane control hero.
but do keep these points in mind.

1) keep warding
2) keep TP to help to TP to save core and carry
3) keep your eyes on minimap, exploit hero gaps
4) if u are mid, always make sure rune is taken by u or by support
5) if u are tank, make sure all is going to push, then go and play by objective, get twr then retreat
6) never give away a free kill, even if u are winning the game

hehe, same here. yesterday, 4 support 1 core. gg no carry.

peaceful games, most are won.
then chii ask u, what hero do frequently use, got more than 50 times?
did u master the these following things:
1) hero movement speed & turn rate
2) hero spell cast range
3) hero armor & hit animation
4) hero compatibility with other hero
5) unique play styles to counter each enemy hero
6) item builds to accommodate carries and cores

and many other factors, if these are not mastered, the hero u are using is lacking in control and will definitely screw up critical moments.
yes, maybe boring but even after playing 600 games of CM, chii still see and learn new things with some heroes.

why drop so much??

well if u just play normal pub will be better. don't drag down mmr games.
pub game also uses current mmr to find games, so u will still be playing good competitive games.

sometimes funny to see mid playing like support role and the support playing like carry style.
all parts and parcel of pub