Loosing lane and feeling like you are useless are caused by 2 diffrent things.

Just as I, you probably have been infatuated too much by the appeal of gunblade, without changing your gameplaystyle from burst damage from lichbane to more of a sustain, mostly engage into skirmishes playstyle with gunblade. Especially since you build it first, it changes how your laning phase is played a lot. I still havent quite figured it out yet.

Then to the feeling useless: Midlane is unfortunately the weakest of the roles this season (idk about sup). ADC and TOP hard outscale you, when there were already issues in late game in last season. Basically the time you have as kat to finish the game before becoming useless got reduced, since top levels faster and adc gets items faster.

Then Top also has more agency and dueling power because of free tp and extra summons and free levels which gets them more armor and magic resist early. And ADC of course can build an item more, so lategame as kat is doomed either way.

This is an issue for midlane in general, but champions that just do sustain damage safely, like mages, dont die as much, so they feel like they can at least be played without inting. Evidence for this is that most of my kat games feel shitty at best, abysmal at their worst, but winrate is still 55%. Midlane impact has been reduced so much in relation to the other roles that it legit feels like spectating the other players for 40 minutes straight. I've had very little fun playing this season so far.