When you say that people are "using this form directly without comparison", that isn't really true. You are ignoring context. Sentences don't happen in a vacuum. So in your three examples, the people having the conversation know what the "other" group/problem/version is. But it's not necessary to mention it.
a larger group (than the one we're talking about)
a bigger problem (than the one one had before)
a newer version (than the old version)
You may like to review these pages on comparative adjectives