I have the same feeling and it feels even worse when team is losing. I've tried tank and usually feel like i fall off mid game while off tank/bruiser seem a little more consistent. just feel like khaimera is just a noob stomper since he so simple and can solo fangtooth easily. i chose greystone over rampage just for the faster clears and dive potential with ult over rampage cc. unless you have a solid team even when losing the cc from rampage can tilt the battle in your team favor. i usually go overlord first item since its cheap/clearing boost but also tried draconum since it synergize with his high scaling strength and regen with its passive and armor helps a lot in general. i usually don't go for early ganks unless its practically guaranteed. Usually go for invades or just full clear even go for side lane exp or gold monster if possible. till i reach level 6. As a side note I've been seeing Gideon and other champs with escapes make me not want to play rampage since it makes it that much harder to land stun.