The F-35 isn't borderline invisible, it can still be detected by lower frequency radars and, by day, optical trackers and contrast trackers - the opposing force will know what is coming. But its LO capabilities degrade targeting radars, increases its JtoS ratio for EA and provide a good host to sensitive ESM systems and weapons for direct attack. Off board sensors, speed and manoeuvre provide the rest.
Can this be done by a larger aircraft - clearly yes and the US has the B-2. Its increase in size provides a better capability against low frequency search radars, so the opposing force is less likely to know what is coming, but it trades away speed and manoeuvre, but increases loiter and weapons carried. Rather more expensive per copy though.
A larger platform has some advantages, but will not operate from tactical locations or ships. For an adversary grappling with an F-35 will be a challenge, even with a reasonable picture of where it is. Add in the potential complications provided by the B-2, F-22, stand-off and stand-in jamming, EA, stand-off weapons and decoys it will be a nightmare to deal with.
With the F-35 once the IADS door is kicked in it will become a tactical bomb-truck that can protect itself.