Well, I do agree that languages back then would have been more complex than they are now. Over time, people would have introduced better ways of speaking, writing and understanding their language, and thus slowly reformed the language slightly. Old English had grammatical gender - but since the introduction of the word 'the', speakers of English at that time started using 'the' and stopped attributing gender on nouns, making the English language lose one 'complex' grammar rule (nowadays we don't need to memorise which noun is masculine, feminine and neuter, but when people spoke Old English, they would have to). Of course, English would have also become a little more complex at some aspects as it evolved and lived, but I believe that modern English was more 'refined' than 'complicated' during its time.

Additionally, I believe that English became a little easier today than before in some ways - for example, the use of acronyms and symbols can convey meaning (not only English - many language now have this feature). This is due to technology and/or the environment that surrounded the language and its speakers. Today, if people say lol, or even :D, you may know what they are saying. When English was older and there was no advanced technology, there were no such words/symbols.

So, to be simple, I think that languages do go simpler due to two reasons - the native speakers of the language would try to find ways to allow them to speak and understand the language more easily (humans don't like to learn 50 rules at one - as opposed to machines who don't even care if you throw 100 rules at them, or whatever), and that languages would try to make itself compatible with occurrences and the environment around it (in the 1800s, many people who spoke English may have believed that speaking in posh and in a sophisticated way was deemed correct. However, nowadays, the idea that everyone is equal is enforced and that people try to use slang and contractions as much as possible (usually when talking online to friends and family) - so now people type 'lol' as it is much quicker and easier than typing 'laughing out loud')

P.S.: I must have written some incorrect information. Please forgive me as I was rushing as I was typing this. Also, you don't need to agree with me. This is just my point of view - I respect other people's point of view as long as they justify it.