Many of the famous inventors and thinkers of the past are simply the ones who became famous. They were not the only ones working in their areas of expertise. Galileo became famous because there's a tragic story behind his name. There were other people just as smart working with lenses. Somebody else would have figured it out in roughly the same time period. Telescopes would be just as powerful today if Galileo hadn't improved upon it in the past.
I think Galileo made a lot of great improvements to the telescope and the world of science. He is responsible for a lot of what we are able to do today. However I think if he were never around it was only a matter of time before someone else came up with the improvements so we would be close to what we are today either way.
Of course, telescopes would be as powerful today even if Galileo had not improved upon them. Technology has a way of catching up, even if it is not advanced for a long time. Although Galileo's discoveries were important, it is likely that someone else would have made them sooner or later.
While he didn't invent the telescope the improvements that Galileo made to the original Dutch designed telescopes greatly increased the viewing power. The first telescopes were able to magnify objects by three diameters. Galileo was successful in designing and building telescopes that were able to magnify objects by thirty-three (33) diameters.
No, I do not think that telescopes would be as powerful today without Galileo's improvements, because he did a lot of great improvements and was ahead of his time. Other people came along after Galileo and built upon the things that he did, but Galileo set the stage for those after him.