If we’re talking about ‘what will go on your gravestone’ then frankly I’d say ‘lived a full and fulfilling life.’ And work life along with family, friends , hobbies is part of that
So, if you’re really not happy in your job, then do whatever you can to change things, retrain, get where you want to be. Generally, more senior roles tend to be more interesting and stimulating (and ironically sometimes more flexible too.) Work is too big a part of most people’s lives (unless you’re born into such extreme wealth you don’t need to earn a living) that it makes sense to aim for something that leaves you feeling good as well as paying the bills.
Personally i dropped to 3 days when my dc were tiny, and that was about me wanting more time at home so perhaps a little selfish in a way, though having said that ML was very short back then so I think full time would have been extremely tough with a 12 week old baby. Also there wasn’t even paternity leave, never mind shared parental leave so things were much more down to the mother.
I stepped back up to full time when youngest turned 4 and tbh it’s great- the opportunity to get promoted and also paying into my pension. Like others, I don’t want to be knackered out and still working when I’m 60 (though I’m planning to always work part time whatever age as I’ve seen too many people decline when they give up completely.)
Try to look at the positives of full time work. Frankly I believe anyone not clocking up enough years is nuts as things are only going to get worse with pensions
And if you really find your job a grind- do what you can to change