Just my opinion, but I don't believe SP Page builder depends on any template based on Helix - you don't have to use Joomshaper templates at all. I quite easily buld a site with SP PB in Cassiopeia, the J4 default template.
Are you perhaps downloading the templates that are a "quick start" package, that may well include SP Page BUilder in the package? (all Joomlshaper.com templates are of course Helix based since Joomshaper is the develper of the Helix framework)..
Don't know what you mean "the templates are old" they seem relatively updated to me (e.g. no later than 6 months old).
You can use any template from any template provider you wish, except I suppose that with other similar frameworks like T4 and Gantry, but I suppose you could try SP PB with them.
As above, a starting point for learning, use the Joomla default template.