yes, you get engine braking, but what you are mitigating is the sudden rpm difference (and resultant sudden tire to road speed differential) that causes the axle tramp and snap spin... the game does this perfectly, otherwise you would see many folks speeding off backwards into the weeds on corner entry.
watch any replay of the faster guys (or even slower guys like myself) and you'll see them downshifting while braking and turning in hard... in the real world any mismatched rpm match/clutch engagement will have you looking in the review mirror to see where you are headed.
In today's televised motorsports most everything is sequential shift with computer controlled rev matching, but, if you really want to see how critical this is watch NASCAR when they run a road course... no electronic rev matching, clutch activated only buy a cable/pedal/foot throttle only by a rod/pedal/foot, faceplated/straight cut transmission, no traction control, no abs...
These guys need to be perfect every time... and you'll see lots of what happens when they get it just a little wrong.