Just sharing my experience in SSB II Mid last year. Mostly followed the plan and then cut out the Wednesday ride each week. Went from 249 to 259 in that block. And that was with a 1 month old at home at the time. So no question you can still get faster over a block if you’re skipping those.
Though looking back, I do think there were some end-of-race aspects of my fitness that suffered because I wasn’t putting in some of that endurance time in my base phase. As I moved into build after that, I’d feel strong during my longer MTB races in the first 75% but as I got towards the end I was more susceptible to cramps, which I had never had a problem with before.
6 months later as I’ve added those back into my routine I’ve anecdotally seen a decline in that end-of-race cramping.