photopoeth

Testing on a Cintiq I'd still say that (Ctrl+Spacebar based) Zoom and Pan work and feel inferior when compared
to Photoshop, unfortunately. The same is true for interactive brush size/hardness change. I wrote about these
issues here (last paragraph) and here.

Thanks SrPx, seems like a great workaround and a universal tool in general. The only thing I don't like about it is to have another tool to configure and keeping in mind when e.g. changing your computer. Nevertheless a great tip, thanks.

You are welcome :)
I know... However, I keep installing my few "favorites" anyway: Irfanview, Notepad++, WindirStat, Thunderbird... They've become just as important as setting up the wacom driver, to me.. ;)
And the laptops are having those as well. :) [i've got none, but my family, each member has one, lol... ]
 
I just resorted to that when I realized that configuring each software the most similar possible in terms of shortcuts and mouse, it was going always to be needed to pan or zoom differently in one or another application. And I did not want that. I'm flexible to go back to that, but I realize am faster working, now. Also, I avoid so dealing with configuring again and again shortcuts of any new installation of the same application -ie, to a new version upgrade-  as x-mouse button deals with that app and ctrl+wheel, for example, and those defaults rarely change.(when they occasionally do, I just modify slightly the config in x-mouse for that app, like I'd do in the Wacom panel. )
 
Might sound unimportant, but I was getting a bit angry at times when wheel zooming at irfanview and jumping to a new file instead -really bad when you are browsing between very large images- . Now it just zooms :)

Thanks James - this definitely helps. BUT... as I am using a Wacom tablet it would be great if this could be reconfigured.
In Photoshop I am used to ALT + RightMouse (RM) and this works great with a Wacom pen (with one button configured as RM). 
Now I don't know how to use ALT+RM+LM with a pen... 

VERY IMPORTANT UPDATE (21st June, 2019) : Depending on your config or how you'd deal with it, this might have not worked, and the trick could have some issues (NOTHING terrible, it just would not be activated, the trick) if you are not well versed in this utility (or in general with this kind of thing).  Please, check the following post I just did (21st June, '19) , much better explained, better ordered, and avoiding some potential flaws (it is a full step by step tutorial, so, you can totally avoid reading this post, only focus in the link pasted just below ) :
https://forum.affinity.serif.com/index.php?/topic/4987-how-to-change-brush-size-with-keyboard-mouse/&do=findComment&comment=477294
 
=====================================
With X-mouse Button Control, easy ...
I just made it now, out of curiosity. Works great.
[    For the below to work, and ending up with just your Wacom or etc pen being able to change brush size and hardness with no key involved, clicking one of the pen side buttons and dragging, you do need first to go to your Wacom panel (or other brand if has this feature) , add a new application (Affinity Photo) if you haven't it already, so to these configurations only affect when Photo is used.
Then configure one of the side buttons of the pen to have right mouse button assigned. This is pretty a basic thing to do with your Wacom, so you surely know this already, but if is not the case, don't be afraid to ask in this thread .  ]
I explained today general usage here:
https://forum.affinity.serif.com/index.php?/topic/27990-zoom-like-a-photoshop/?p=135701
But for this specific case, is, of course customizing the app, Affinity Photo (Photo.exe) , just in this case is Right mouse button, using again the "simulated keys" option, but then use "during" for the mouse mode, and the codes {ALT}{LMB}{RMB}  . takes 10 seconds, and is only done once, for ever... Until you change it or deactivate the tool.
Here it's working great...
 
Screens (sometimes does not end up loading the image, in that case, right click and choosing "open link in new window", should work).... :




PD: Made it now in a moment, by setting like you, RMB in my Wacom Intuos Pro pen (just for A. Photo in the wacom panel, of course ), then just telling X-mouse how to deal with RMB, as explained in those screens above. Anyway, much step by step explained how to use this free utility in the other thread I link here above.  (and the utility :  http://www.highrez.co.uk/downloads/XMouseButtonControl.htm )
____________________
 
Advanced tip :
 
Addition for those enjoying already this utility (for AP or any other application) :
1) You do not have to block the right mouse button by assigning it to a side button in the pen. As wacom allows it, you can instead assign in wacom panel the middle mouse button, or even a 3rd or 4th mouse buttons in your mouse, if you are lucky to have one of those. This way you leave the right mouse functions free for whatever other uses. I am using the middle button mouse now, and would use a 3rd or 4th if my mouse had it, instead. Using it for all x-mouse layers (configurations) FOR AP ONLY (as in Wacom panel I only set it for AP).
2) You might have noticed you can use layers in x-mouse button. This are simply alternative configurations. So, you can fill up all options on a layer 2, and swap to that config at any time, by just hitting the layer swap button in X-Mouse window, which you can leave open for fast access, is fine. Two buttons: Swap, and APPLY button, so that changes are actually applied and working in AP. No need to reboot AP neither X-mouse. On the fly.
 
This way, am having two configurations: One with which i set my side pen button (set as middle click in my Wacom panel, but ONLY for AP ) to be my color picker, which is for when I'm basically coloring, oil painting, and so picking a lot colors in the canvas. The other configuration (x-mouse layer) is to have my pen side button to do the change of hardness and size change. Useful when I am doing line art/comic inking or pencil sketching.
 
Configuration 1, for brush size and hardness :

 
Configuration 2, for color picker :

 
Swapping the layers to make active the other configuration.

Thanks James - this definitely helps. BUT... as I am using a Wacom tablet it would be great if this could be reconfigured.
In Photoshop I am used to ALT + RightMouse (RM) and this works great with a Wacom pen (with one button configured as RM). 
Now I don't know how to use ALT+RM+LM with a pen... 

That helps not a lot, since it's not as smooth as sliding the pen. This is a lot more intuitive.