The difference is big in metro exodus as you can see here, and that's just very limited RT implementation (sun is the only source of RT GI, so only outdoor scenes are affected, and there's only 2 light bounces, too small to lit evenly high contrast scene)
At 1080p performance is not that much worse compared to RTX off, and 2070S can run RTX effects at around 63 fps (71 fps without RTX), while game looks clearly much better in all outdoor scenes.
Of course current games use limited RT (limited amount of rays and effects), but limited or not, it's still RT, so you should not call it a gimmick, because it's not a gimmick and that's exactly why it's so demanding. You can call RT uneccesery feature, but gimmick is the last word you should use.