You're in error about DL lifetime miles. Only butt-in-seat miles count toward status there. This became the policy when they introduced SkyMiles in 1995 to replace their earlier Frequent Flyer program. Previously, all miles counted toward lifetime status. They left existing lifetime totals intact when they switched, but since then only flown miles count.

You'd think this would be offset by correspondingly higher benefits for reaching MM totals on Delta, but in general it isn't. Both give lifetime first-tier status (DL Silver, AA Gold) for 1MM, mid-tier (DL Gold, AA Platinum) for 2MM. DL also gives lifetime top-tier (their Platinum) for 4MM, but for most of us that's not of much practical importance - it's 200,000 actual flown miles per year for 20 years in a row. At that point they should name at least an airplane, if not the whole airline, after you!