Listen, AS gives you exposure to DL & AA. UA gives you to *A.
At 70k per month that is 1M a year = I would split them up at 40%, 40% and put 20% on an SPG amex
Total cost = 200$ for someone spending 70k a month, that is nothing...

If you want status, go with a biz DL Plat and Biz DL reserve = 50k MQMs = status will help on AS with upgrades and no fees, but you will lose AA.

So you could theoretically do
60k / yr on DL Reserve = DL SM + 1 free companion ticket in F and skyclub access
50k / yr n DL Plat = DL GM + 1 free companion ticket in coach
200k / yr on AS Visa = 1 free companion for 99$ in any fare
200k per year on UA Visa = 5k EQM + misc perks (incl lounge access if you pay more)
200k per yr on an SPG = 30k is enough for SPG Gold Status
40k / yr on Hilton Surpass = HH Diamond status
100k /yr on a Marriott Visa = Status credits for lifetime status

That will give you all you need for travel for about $750 cost after tax. = < 0.1% cost

btw I forgot, welcome to FT!