No, other GOP candidates didn't prove their national electability so far. Trump won once and came close a 2nd time despite a disastrous term.
That said, Biden can easily recover once he starts running for reelection. All previous presidents looked more vulnerable in the middle of their 1st terms than they actually ended up being. Let's not pretend Biden is DOA, even if midterms end up in a sound defeat. Especially if the GOP overreaches subsequently, it can help Biden as well.
2023 and the first 2/3rds of 2024 will decide everything re Biden
If we were talking in 1994 and the first half of 1995 prior to Oklahoma City, it’d seem pretty certain that Clinton would be a one term President. By the end of 1995, it was pretty clear he’d win in 1996 unless the nominee was Powell and once Powell dropped out of the race in November 1995, the wave was paved for Clinton’s second term.
If Election Day was held today, Biden would lose to Trump or DeSantis handily
Let’s see how 2023 and Jan-August 2024 go