If you assume Miyata isn't wrong, then frankly 1:100 chance to win is amazing. Because as far as any other fighter is concerned their chances were zero. Going from no chance to some chance, is the largest step towards winning, from a certain POV.
I'm hoping the next chapter brings Ippo down to earth a bit. I expect him to handle this well, but he won't trash Sendo by any means. The guy is ranked 1st, he's a natural born monster, and he's been training like mad.
Admittedly we are running out of foils for retired Ippo to strut his stuff against. But I still personally believe Ippo will never be world champion as long as Ricardo is. All of his improvements are amazing, but a recurring theme in the series is the existence of limits. The series is more about what men do to get where they want to be and how they deal with what comes after, not about actually winning.
How long has Ippo been retired in-universe?
Uncertain. At least 2 years. He retired in early 1998, and the current date is somewhere late in a year starting with 200X. It could be 2000 itself, or later.