I have a hard time saying Harper is better than Altuve at this point. Pas t 4 years, not only has he racked up more fWAR (24 v. 19.2), but he's also just played more. Harper has a bit over 2200 PAs. Altuve has 400+ more than that, or 3/4 of a season. wRC+, Altuve has gone 137 / 124 / 151 / 160, while Harper has gone 115 / 197 / 112 / 156. This year, most projections have Harper around 150 and Altuve around 140, but he plays a tougher defensive position a bit better than Bryce plays an easier one. Altuve's 2.5 years older, and, given Bryce's age, maybe the best is yet to come, but is he worth $10MM more a year over the next 5 years and an additional couple years of $40 MM beyond that? I just don't see it.
I'd be OK with a deal that offer him $105 MM over the next 3 years, then an opt out, and tacking on 4 more years at a price low enough to ensure he does opt out (say, $100MM). The opt out is insurance for him. It's only not exercised if he's a bust. I don't overpay on that insurance policy. Would I scream if years 4 and 5 are at $35MM and another opt out before payments drop? Probably not.