It's easy for Republicans to feel like the economy is great, bc if they can convince themselves that it is great or about to be great for THEMSELVES, they can say the whole thing's great. Dems OTOH are more likely to remember that it's still shit for many and say it's just OK.
And that's if it's going decent for them. If the economy is shitty for a democrat AND they know it's way shittier for poorer, more marginalized ppl? They'll say it's a disaster, Dem prez or not.