The salaries are ever increasing, so if Rendon and Stras decline the last few years of their deals...inflation of salaries will be so that players the level they may decline to now make the same. Injuries are always a threat, especially with a pitcher, but Stras has the stuff and location/savy to be effective for many more years, ala Verlander. He already has lost the high 90s heat he came into the league with. He can be very good at 93-95 with his pitch mix and location.
Rendon has a skillset at the plate that I also believe will age well into his mid-30s. I don't worry about giving Rendon 7 years and Stras 6.