I think this all boils down to CantonJester just not being aware of the way that extensions are agreed upon with relation to service time. Everyone learns it sometime, now is just your turn
Guys simply do not get paid FA rates for the years under which they wouldn't have been free agents. They are reduced based on if they are pre-arb (first 3 full years), Arb1, Arb2, or Arb3. Some guys are Super-2 which makes it slightly different but let's ignore that for now.
For an example lets look at two recent mega-deals, Fernando Tatis Jr and Francisco Lindor. I think it's fair to call them comparable players. Lindor signed for 10/$342M, and all 10 years are FA years (he was already one a 1-year deal for his final year of arbitration eligibility). He was only one season from free agency, so there is very little discount given for signing early.
Tatis signed for 14/$340M, which is only a $24M average, but that's misleading because he had 4 years until free agency. He'd have gotten near the minimum in 2021, then Arb1, Arb2, and Arb3. Let's use Hallas' 40/60/80 model for those arb years (and 0 for the pre-arb), so the $340M he's gonna make over 14 years really is covering a net of 11.8 service years, so $340M / 11.8 = $29M. Because Tatis was so much further from his own free agency than Lindor, he had to give a bit of a discount on the value of the FA years to get the deal done, as otherwise the Padres would be taking on all the risk with no reward.
So, as for Means, come up with whatever number you think he's worth if he were a free agent. The best guys make about $35M, but they have a much longer track record than Means and better production than Means has had to date. Do we wanna say $25M? $20M? Whatever it is, reduce it by a bit because he's signing 3 years early. I'd say a 10% reduction is reasonable. So $23M or $18M depending on your earlier evaluation. The contract he'd sign after this year is 40% of that for Year 1, 60% for Year 2, and 80% for Year 3. So 9.2 / 13.8 / 18.4 or 7.2M / 10.8 / 14.4 depending on above. Then add in the full rate for FA years.
This makes the a total contract of 5/$87M if you think he's a $25M pitcher. Or total contract of 5/$68.4M if you think he's a $20M pitcher.