Does this make a weak musician?

It makes the song uncomplicated. It may still be catchy and have a great hook. It won't have depth and it won't have much texture. If it's three or four instruments and runs under five minutes, though, it doesn't matter that much. Dream Theater had a lot of accomplished musicians, but the Rolling Stones held their popularity for much longer with a lot less going on in their music. A four chord song is a very weak effort at a symphony, but a symphony is a really weak effort as party tunes. It depends on your audience.