Any mitre saw stand will only take timber up to a certain width, before it can get unstable.
I have a few mitre saws and stands, including the Kapex and UG base etc, and they have all been fine cutting long lengths of skirting, trims, mouldings, right up to floor joists and trusses, that are thick and wide, and because of pressure treatment, heavy.
No problems with any of the saws, or bases/stands. Any of these set ups can have extra support applied if needed.
Setting up, get the folding base for a 10” or 12” Makita mitre saw off the van. Set the base up, go get that big saw off the van and carry it to the base. Lift the saw onto the base and lock it up.
Kapex and UG base: get it off the van, wheel it to the work area, unlock the tab, put one foot on the base, lift the saw just below the cable tidy, guide the support leg into the slots, lock the the tab. Fit the extensions if required.
Which set up, do you think will will cause, or aggravate any back issues? [scratch chin]
I willingly fetch the Kapex off the van, the other saws, I let somebody else have the privilege [wink]