If I remember correctly, Celebrity was using lavazza or ily coffee in the percolators (a european/italian dark roast) for drip coffee. Espresso beans were a similar dark roast style. (Eq, July '16, Silhouette, Feb '17). I like that style coffee (and don't really Starbucks beans other than their blonde roast).
Coral and most of the Princess ships use coffee concentrate in the MDR and buffets, quality is variable but it's weaker and lighter roast style coffee (I haven't sailed Regal/Royal, but word is that's fresh brewed there).
Brewed coffee at the IC was fine, again weaker side and lighter roast, not my style but fine (think freshly opened folgers/maxwell style coffee). Same lighter roast beans were being ground for their espresso drinks (Note: I got a scoop of beans and was huffing them for an hour during the wine tasting... so I paid a lot of attention to those beans ). Using that lighter style roast will give a little less depth than a traditional dark roast espresso bean, but beans were ground right at time of tamping for shot to be pulled. Milk was steamed in front of you and then latte/cap was poured there. I don't remember them using a thermometer on Coral, but temps were definitely hot but milk was never scalded (assuming no thermometer though it'll depend on who steams your milk as to whether they overshoot).
Princess (x4): Coral (5/2017, Alaska), Ruby (12/2012, Carib.), Crown (4/2008, S. Carib.), Star (4/2007, W. Carib.)
Royal Caribbean (x3): Jewel of the Seas (12/2013, S. Carib.), Monarch of the Seas (12/2008, Bahamas & 2/2001, S. Carib.)