[Startup Financial Planning] Build a tool to analyze startup equity offers

Just getting into startups lately, I've been interviewing at a few across pre-seed all the way upto Series D. Hoping to get input from smart engineers who have been around a while and played the startup game. I have a startup offer from a Series D unicorn ($1B+ val) with a ~250k base, 0.039% equity (~450k in paper money). My biggest concern is, the strike on the ISOs is high enough to be prohibitively expensive ($100k+) that I can't exercise without a liquidity event, and this company has a 90 day post-termination exercise window. So if I leave pre-IPO (voluntarily or not), those shares are basically worthless. Not such a big deal if liquidity is soon, but the recruiter says the founders' exit strategy is to IPO at $8B valuation in 3-4 years. I did some modeling based on the ARR and profitability data/forecasts I got from the recruiter, and realistically the company's valuation would be $3B-$5B in that timeframe. $8B is too premium a multiple, that I feel is unrealistic for this market/company. So, I'm not sure sure if the founders would still IPO in 3-4 years time given; and if they delay, I likely don't have the appetite to stay long for 6-8 years because the cash comp from the startup is a paycut and every year delayed will compound the deficit. What would you be thinking about if you were me? Advice on how to negotiate this to make it work? Is their offer fair already, am I supposed to just take a leap & hope for the best? Thanks!