Cap is going up more than usual in 2021, and will probably increase more than usual every year afterwards as they divvy up % revenue splits, and NFL making record revenues across all the sectors of the original deal.
So, the real question is, if you DO tag him, that tryout year on the tag will immediately erase $13m in extra cap for 2020, as his first year deal would have otherwise been about $20m, as opposed to $33m guaranteed on the tag.
But also, the whole "tryout" year to see if he earns the spot, if you actually decide to keep him, that $110m guaranteed just turned into about $150-160m guaranteed and is a $200m+ over 6 years, because you gave him $33m guaranteed on the tag for one year rental, and his price just went up on his contract. Tag + deal + cap going up.
Or, he doesn't earn it, and God help our souls if Jerry Jones has 1st round picks trying to find a QB. Now you're in the "search", how many premium picks would that be? Would we rather have those picks, with a new coach, going to BPA and using cap space on Dak? We also run the very real risk of a new coach, who actually might be halfway decent, getting handed a huge risk in a rookie QB, how long does that coach last if the guy just isn't very good? That happens. Quite often.
For me? Depends on the coach, I guess. Give me someone who I think may be able to Shanahan it up, or any halfway decent coach that actually gameplans with his weapons, Meyer would probably work. I'll use the cap space for Dak, and use my picks on BPA, with cap heading north. I think the team is underachieving, and I think if we got someone in here who could coach worth a damn, was willing to cut Crawford, and actually emphasized getting some talent at DT, S, coaching these guys up, and getting them prepared for real NFL games, Dak would be just fine.
After seeing what a discombobulated mess this entire team is, I think Dak can only improve under a coach who can get at least one unit on the team playing halfway decently.