Well, yes they are right. You CAN. But for a few reasons I consider valid I prefer to do my slow paced accuracy rifle loading on my single stage.
Reasons include not needing a caliber conversion and additional spare die plate. Around $100C for a 650 or 750 caliber conversion currently. So only a couple of kits and you can buy a pretty nice single stage. And that's before you buy a spare die plate or two.
On top of that I prefer to decap the old brass first without sizing THEN clean. Putting clean and freshly lubed brass through the sizing die is just a better option. Again this CAN be done on a 650 or 750 for those familiar with them. But I just prefer doing it more out in the open on my single stage.
There's some really nice heavy duty singles out there but in the end I opted for a Hornady with the breech lock bushings that make switching dies fast and consistent. So that's a big plus for me. Now since that time I must admit to drooling over some of the heavy duty singles. But really my Hornady does just fine.
If you do opt for some other brand without a breech style I strongly recommend the Hornady split adjustment nuts that pinch lock around the thread. If you opt for the option of screw in dies these lockable nuts ensure that they don't shift and will seat consistently and hold your adjustments. You can buy those Hornady nuts separately in bulk too. A nice option for any screw in based press or for the Forster press that uses plug in dies with the nuts acting as motion stops. Keep it in mind as you're shopping.
If you buy a press other than Hornady and if it comes with the larger size thread for large dies and uses a bushing for the 7/8" standard dies then you may want to know that bulk packs of 10 Hornady breech lock bushings come with an adapter that screws into the larger thread size in the press.
Admittedly I've gotten use to the rapid switching of the breech lock system. I've certainly drank the Hornady Koolaid on this one feature. But it does work for me and I would not buy another single that could not be adapted to use these bushings. Take that for what you will.
Later on too if you find a need to break down some ammo with a collet style puller a good single stage again will serve well. It's just easier to work around a single than to work with a big assembly of a larger size progressive. Basically however you reload having a single around does have its place and will prove to be handy for some things that the progressive CAN do but which end up easier on the single. Not to mention that if you do your accuracy rifle loads on the single you don't need to break down the progressive for what is often a short batch of loading.
I'm lucky enough that I could buy pretty much whatever I want. But it would only be for the BLING factor. My 550 serves ME very well for my needs. And having a single stage alongside covers off the way I prefer to load my accuracy rifle.
I'm not trying to say buy this or that. But I would say that from your last post above with the amount of ammo and what I'm sure is a desire to spend time with the family that if you can spare the cash that a somewhat faster progressive sitting alongside a decently handy single stage would very likely serve your needs as well.
That's a fair bit of rambling around but as you start to shop around for options I hope it gives you an insight on making your own decisions.
It's a big outlay at first. There's no doubt about that. But after 15 years of reloading I figure I paid off the cost of all the gear at around year 5 to 7 in terms of cost per 50 rounds saved vs buying factory ammo. Since then it's not only been a significant savings on ammo (at a cost in time of course) but let me work with calibers that are simply not common. Namely .38-55 for my single shot peep sight rifles and more recently .44-40 for my cowboy action shooting. Also I load my own black powder rifle rounds for times when I shoot cap and ball pistols in some of the cowboy action events with the .44-40 in the rifle. And black powder shot shells from my side by side.... I've never seen the second target. Just move over, pull the trigger and hope...
Cheers