"Are they better than HMS Ocean or the two Albions or are they too different in their design and intention to draw a direct comparison?"
"Ocean" - LPH 1998 22500 tonnes 17 kt 12 Sea King + 6 Lynx; 285 ships crew+ 206 air support - max 1275
"Albion"- LPD 2003/2004 18500tonnes 18 kt 4 landing craft + 2 Chinook sized spots 325 ships crew + 303 to 708 troops
"Mistral" - LHDM/BPC -2006-2012 16794 tonnes 19 kt 4 landing craft + 6 spots for CH-53 or Osprey (hangar space for 16 Puma) 160 ships crew +400-900 troops
so a lot cheaper to man and probably the same as Ocaan & Albion in capability - but you get both in one ship
TBH we'd be better off with 4 of these rather than the QE class carriers