hi! I made an entire section about this in my fishing guide [ Fishing - A guide [V1.14] ]
TLDR; Youre overall more likely to get a sunken by banking on the pity rate. The pity rate is a function in the game where, upon your 2999th fish, the 3000th will always be a sunken.
The easiest way to achieve this, and easiest way overall to fish for sunkens, is a bronze rod with luring [or its T2 equivelant]