One thing that can be done to ensure consistent cuts is to change the blade when needed.
That being said there is zero difference in the mechanics of a Lighthouse vs Showgard vs Fiskar cutter. They all have straight edges and guillotine or rotary blades. You can put a Ferrari nameplate on a Chevy Bolt but you still have a Chevy. I would wager that Fiskar manufactures the other "brands".
I have a 20-year-old Showguard cutter that still works like a charm. A couple of years ago I won a Lighthouse cutter in a contest that I was happy to receive since it can handle the larger size of mounts. The damned thing mangled almost every mount I tried to cut with it so back into its box it went where its now collecting dust. For the larger mounts I still use my Hawid hand cutter that I got back in 1968 (!)(with the occasional blade change, of course).
I have the Lighthouse & use it for most things - it's smaller than the typical craft cutter like the fiskars. I use pre-cut black Scott/Showgard for single US stamps, but use clear Hawid strips I cut myself for international. I also have acess to very large cutters my wife uses for scrapbooking, the largest Dahle is probably 2 kg/5 lbs. I use it to both trim old frayed album pages and souvenir sheet-sized mounts. I also make craft foam spacers for 2-post binders on it.