Not interested, but was there "way back" in 1994. Mountains don't change much. When we were there there was a major hut on Chimborazo WAY HIGH, I forget the actual altitude but we climbed about 200 vertical feet above the hut and that was, at that time, my personal high altitude. I would have to say the hut was at about 18,000 +/-ft. (We had just climbed 17,6000 ft Tong....??...close to the town of Basas [Bazas?], and the Chim. hut was higher, or close to it.) In any event, the summit was considered a day climb from the hut. I do remember my friends, who spoke excellent Spanish and had been living in Quito for 2 years, had to ask 3 times for the correct road directions, but you drive to the hut.
Perhaps your acclimatization period is too aggressive / too extensive. If you "acclimatize" in Quito, or anywhere else, "watch out for the water" (and anything else uncooked, e.g. salads) After two weeks of absolutely neurotic measures to "drink & eat clean" [our friends had been doing it for 2 years ! ] we went to the best restaurant in Quito on the last night to celebrate, and I had a scotch on the rocks....next morning..day..next week...well let's just say this this was pre-911 and in those days you could go to the bathroom in airplanes pretty much right up to landing...I think I made 6 trips. I have alwayes felt the ice cubes in the scotch was the culprit!
Maybe a couple of "careful" days in Quito, some easy hikes, then one of the 14-16,000 footers, then go to Chim. If you're "pushing" the rainy period, maybe the extra days just wait for your weather window?
I forget the exact name of the 17,600 ft-er we climbed down by Bazas[?] but it was a good hike. Afternoon hike to a primitive hut, then up for an alpine start (2am??) and up to the summit, which at that time was a bit sulfurous. Then down, pick up gear at the hut, then to the car. Great views East to the Amazon Basin at dawn.
If you do hire a local guide, when we were there (granted 25 yrs ago) the BEST "tip" was to leave the guide any old climbing gear: old rope(s) / even 7-8mm cord. Then, stuff was almost unavailable and horribly expensive (in "Sucra" terms, not I think they use the US $ ). I left 50 ft of old 7mm with a guide we befriended at the hut, and it was like I gave him a $1000. I don't know if that has changed or not...perhaps someone else knows?????
If you decide to do Cotapaxi, stay at La Hassienda Cenigal (spelling is all wrong) and book the Humbolt room, if it hasn't gotten too expensive.