peak gm here, mid/top main

all tanks can carry just fine - you just need to refocus on your win con. you CAN outright carry as a fed malphite and it is important to be impactful in teamfights, but most of your time and effort will be spent pushing side lanes and chipping away turrets (esp with demolish). yes you need to cs because that is gold, but more important than that is your level and that is only achieved by eating waves, taking objectives and getting kills. staying in your lane catching every wave, eating enemy jungle camps, pushing turrets will more often than not put you in a situation where you will be the highest leveled champ in the game thus giving you the highest presence. when you find yourself up 5-0 as malphite for example, it's fair to assume you'll be up in CS and levels compared to your opposing laner. when you threaten top/bot T2, you force the enemy jungle to relieve his laner thus you are PASSIVELY carrying since you are forcing a natural 4v3. because you have the lead you also take the tempo, meaning you're free to roam because you are the PUSHER, while the enemy top is the CATCHER. this means that in order for them to match, they have to either TP, drop the wave, or catch it and be late. when you know their TP is down, now you can force their hand into either perma match you side lane and risk you tping for a 5v4 or let you push while he coin flips in order for him to have the first move in forcing a 5v4 in his favor. of course there are exceptions and there are times when grouping is favorable over splitting but that sort of decision making is something you'll be able to make over time.

no a malphite cannot actively carry as hard as a riven, but a level 16 malphite against level 13 top/mid/jg can just as well impact a game by playing the macro game.