Not only is it is fundamental biblical doctrine
As is common, you far overstate your position and in so doing, make a false statement.
You are welcome to believe in the pre-tribulation return, but it most certainly is NOT a fundamental biblical doctrine.
A fundamental doctrine is one that distinguishes a Christian from a non-Christian, a cultist, or a heretic, etc. Fundamental doctrines include the deity and humanity of Christ, His virgin birth, His sinless life, His atoning death, His resurrection, and His return.
Specific claims as to the nature and timing of His return are outside