I can attest that spelling is far more difficult than reading. In fact, the program we use as remediation with DD completely separates the two, recognizing that reading need not be bogged down to the pace of spelling (DD finished All About Reading several years ago. I think we'll be working on All About Spelling forever....). Eventually, you can learn and apply all the rules of reading in English. Most of spelling, however, is just memorizing. (For instance, you can learn to recognize/ read the many ways to spell the sound "oh", but it's usually random whether it's spelled mote or moat.)
With respect to your DS, here are the possibilities that come to mind:
1) His spelling is perfectly normal, just not keeping up with his highly-accelerated reading
2) His spelling is developing normally, just more slowly/ with more difficulty than some
3) He is dyslexic
4) He is dysgraphic - as spaghetti flags, definitely worth looking into given what you are seeing
5) He has auditory processing weaknesses related to the ear tubes, which can cause dyslexia-looking problems connecting sounds (which the brain isn't processing quite properly/ consistently) to symbols
Given those possibilities, you might want to look into testing for phonological weaknesses, handwriting automaticity, and auditory processing (not a normal hearing test, requires an audiologist who specializes in this). Note that any of 3, 4 or 5 could be present in combination, which makes things harder to tease apart. Acting sooner is way better than waiting, so it's worth paying attention to your and his teacher's gut feelings.
Some things you can consider at home with respect to (1-3): is his spelling consistently phonetic, or is the order of sounds often a bit scrambled? Does he spell the same word differently at different times? Does he read aloud happily, or with resistance? Reading aloud, does he skip small words, prefixes/ suffixes, people's names; substitute words with plausible alternatives that start with the same letter; or not recognize a word he read earlier when the context changes? Can he read a list of individual words as easily as a story? How about nonsense syllables? I would note that it's amazing how well a kid that age can fake reading, using a mix of memorizing word shapes, context, pictures, etc., so it's important to look into the underlying skills when stripped of all those helpful hints.
For (4): Does his spelling seem better when he types? For (5), does he often seem to mishear things people say to him? Is it worse in a crowded environment? Does he consistently spell certain sounds in odd ways, like he is hearing them differently? (here's a good APD intro:
https://kidshealth.org/en/parents/central-auditory.html)
Something to think about: a good phonological-based reading program like All About Reading can be really helpful for all kids, not just those with dyslexia. About 40% of people actually need to be taught sound-symbol correspondence in a more explicit and systematic way than schools usually do, in order to become good readers. So regardless of whether it's a lag, a slight weakness, APD or full-blown dyslexia, you may find it helpful to use an explicit approach to teaching reading and spelling. One thing I really like about AAR is that it builds in the ability to do as much repetition as needed, but is easy to move on when you don't. The worst that can happen is he blows through the program at light speed, and you shorten the frustrating period in which his writing can't keep up with his ideas.
