If you don’t pronounce it ‘Yoolius Kayser’ you are guilty of perpetuating one of those English mispronunciations you are railing against.
The only way I can think of that this mispronounciation could have come about is if some English person who had never heard Latin being spoken just read the name as he thought it looked and passed this error on to others. The change in pronounciation could only have come about as a result of confusing the hard and the soft uses of the written letters ‘j’ and ‘c’...
C and cc always confuse me in Italian - I never know hard from soft, I always get it wrong. That being said, I stand by my castigation of Brits awful torturing of foreign words into English words. This is not about MISPRONUNCIATION. It is about strategically mangling the language. It’s pure British xenophobia.