Grinder first, then maybe the machine? Bambino Plus + super budget grinder, mostly oat lattes [€2000 total]

coming up on about a year on a used Sage Bambino Plus and a cheap grinder (Emilio 152CQ300: 40mm conical, 31 steps). 1-2 oat lattes a day, occasional straight shot, occasional back to back.

Lately the shots just land flat. Not sour or bitter exactly, just dull and different every time, and steaming feels slower and weaker than I remember. The machine came to me used so I have no idea what it went through before. Since I've had it: weekly backflush, descaled recently. How do you know if your Sage/Breville is at the end of its life.. or if its damaged somehow?

Regardless, I'm leaning towards upgrading, and it seems like any upgrade in the espresso machine will need a better grinder so:

Grinder: I want to buy once. DF54 and Niche Zero are the two I keep seeing

Machine: I keep circling the Profitec Go but I'm not sold.. the Bambino's thermojet steams instantly and the Go makes you switch modes and wait. Feels like paying for better espresso and a worse latte workflow, and lattes are 90% of what I drink/ On the other hand I do want to lean into espresso more than I have been, so maybe that trade is the point. Is it better long term to consider Is adding a bit of extra cash for the Diletta Mio the move? what is the consensus on these machines

Happy to hear "sort the grinder, get another Bambino, buy better beans." Also happy to hear I'm wrong about the Go. And if there's something obvious I'm missing in this range, tell me.