I'll give you this as a free agent, as this year I decided not to be loyal to any airline: Delta has the best end to end product of the US legacies. I've chosen them more this year as a result.

It is very true that Delta is actively trying to monetize the front of the plane pretty aggressively, but so is every other carrier, even if they're not as up front as Delta about it. Plus, on those occasions where I've sat up front (first or E+), Delta's been better than its competitors, to me anyway.

Delta very much prefers to sell you the exact product you want, and upgrade opportunities are drying up, but as someone who's paid for first ~50% of the time this year, Delta's the only domestic carrier where I'm willing to pay for it. It's worse for elites on every carrier, but that's what airline consolidation has done.