that can happen if you use a terrible theme but you provided 'no' details so it's not possible to help you out unless you tell us what door you came in.
1.7 done correctly should increase seo, in content (attributes now in url) and speed (technical seo)
i'm suse you ran 'some seo tools' but if you don't know reason then you only work in voodoo, you should look at visitor experience, technical seo is something you can create tasks to address....