It is also no secret that Delta wants control of their own brand which is mostly controllable with Endeavor. RJs are a necessary evil for now. Ed recently stated that he is “happy with the amount of RJ flying Delta has.”
Source: https://www.reuters.com/article/us-delta-air-ceo/delta-air-lines-happy-with-pilot-contract-rules-for-regional-flights-ceo-idUSKCN1N02WB
The A220/717 combo is going to be a big deal once it’s all said and done with respect to large RJ flying replacements. Delta pilots will not be giving an inch of SCOPE in upcoming negotiations.