After reading until chapter 44... I can proudly say, this series could've ended in 1 or 2 volumes of around 15 chapters with around 40 pages each.
Well, resource allocation mechanics wasn't specifically was never stated (from how I read things), so my further critique is kinda biased. Additionally, he could've summoned all his beasts to the point of having no stones left or at least 1/4 left and let them rampage and call them back. Imagine, using up a lot of resources to summon dragons and straffing millions of demons equalling to maybe trillions of exp. EZ level up and rank up. Using those ants to make smaller ants. Summoning exploding rocks and bombing demons from the sky. It cost's stones to summon, but I don't think it costs to use their skills. Unless he's summoning them, letting them use skills, then calling back... which is very stupid. Again, as I said, this could've ended in a volume or two.
EZ no brainer move. Maybe he could've defeated the demon lord when he reaches 15 years old. He could exploit the kingdoms and other authorities to provide him with stones and he could summon almost infinetely. Plus, other beasts coul multiply or birth smaller monsters.
Also, although more of a personal experience from RPGs, summoner classes are by far one of the easiest classes to use even with 'Hell Mode' activated. And that's what's happening here. True, he started out in a harsh environment but now the series is something similar to Kenja no Mago.
Don't get me wrong, I like the series, giving it a 6 or 7. But the execution is kinda dumb.