With anchors, generally I like the idea of the bigger the better, but you have some constraints to contend with in the design of your current vessel. It's quite a leap to go from a 45# to 73# anchor. Can your windlass and other deck gear handle it? A simple crude test you can do is to add 30 lbs of weight to your current 45# anchor and see if your windlass can haul that dummy anchor up and properly stow it.
A Rocna will often come up loaded with a scoop of seabed, especially if you anchor in muddy bottoms, so you can estimate occasionally having an additional 10-15 lbs added to the deadweight of the anchor. So, for good measure in the test, add more weight, maybe a total load of 90 lbs for the anchor alone, (plus the chain of course).
Your windlass should easily be able to haul such a load up to the boat. The problem tho is at the turning point where the anchor stock rolls over the bow roller, assuming you still have the original anchor roller from Hunter. The force required to pulll it over that sharp 90 degree bend is considerable and may well be beyond what your stock windlass is capable of. The bigger the Rocna anchor, the longer its stock. As it swings over the bow roller, there is a chance the longer stock on a bigger (33Kg) anchor will hit your furling gear. Check that dimension for fit. Also, check chain sizing recommendation for the Rocna 33. I think it's 10mm, or 3/8". Is that OK with your current windlass?
Before buying my Rocna 25 (55#), I first checked the dimensional fit and then did the windlass test by attaching some old 10# barbell weights to my existing 44# Delta. It worked, but that test told me that a 55# Rocna is at the top limit of what my stock windlass and bow roller can handle. Boat is a 2005 H41 and uses a Simpson Lawrence Atlantic 1000 windlass.
You will find one of the challenges of owning a Rocna is breaking it out of the bottom when you are ready to depart (depending on the sea bottom of course). This is a lovely dilemma because it gives you reassurance your anchor is working extremely well. But the downside is it can take a lot of force to break it out. You will probably resort to breaking it out by motoring over it. The larger the anchor you have, the more strain you are going to be putting on your deck gear when breaking it out under power.
A Rocna 33 is going to be big. You can check dimensional fit by building a rough full-size template from a PDF file that Rocna will send you on request.
As already stated by Maine Sail, Rocna is conservative on their anchor sizing, but only you know your intended cruising grounds, bottom conditions and likely weather conditions. And if, considering all that, you need a 33Kg anchor for your particular boat. If you really do need one yet you run in to fit issues as covered above, then you will need to modify your boat/gear to suit.
