Sorry Will but you’re using flawed logic to justify your actions.
Upgrade to FO and then final upgrade to Cap is a natural career progression within any airline, it is what is expected of you by everyone. So long as you meet the experience requirements and the standards, you will be upgraded based on seniority. Nobody is disadvantaged (CX politics aside)! The upgrade is not volunteered for, it is your entitlement. Upgrades are rarely turned down, and if they are, it is usually because of extenuating circumstances.
Taking a training position is as much of an upgrade as volunteering to be a CX flash mob dancer. These positions are volunteered for through NTCs and completely out of seniority. You can apply having met all their requirements and they can still reject you if they don’t like you. You’re simply not entitled to a training position, but you will always be entitled to an upgrade.
An upgrade has a huge impact on pay, experience, and future marketability. It’s the goal of every pilot within an airline to try and get to the left seat as quickly as possible. You’re not really helping the company by taking an upgrade, you’re really helping yourself.
Taking a training position has an insignificant impact on your overall career in terms of pay and marketability. So in a way you’re really helping the company significantly more than you are yourself. So why do it at a time when relations between management and pilots are at their lowest? What are you trying to achieve by doing it? What are you missing out on if you stay as a regular line pilot?