group limit is a server restriction not a Delta Chat restriction, in a real situation where a company or a self hosted email server needs a group to be bigger they can relax the restriction.
Anyway message size is also restricted by email servers in the case of Cuba (Nauta server) the maximum size is 2MB.
following your idea, what should happen if I send an image of 10MB to a group of 30 friends??? first the message is split in smaller pieces and then in smaller groups of recipients??? quite a mess 