Having been to Fiji (near Taveuni) and French Polynesia (Society and Toumotus), I would say the diving is different in both. I personally liked diving in Fiji more than FP.
Bear in mind that my Fiji and FP diving were in only certain spots and that other parts will be different. By report there were more sharks seen off Viti Levu than where we were. FP and especially around Moorea had many more sharks than what we saw in Fiji. FP had mantas and we saw none in Fiji though they are supposed to be there. I saw many more fish in Fiji than FP. In my mind FP was about big stuff - sharks, mantas, dolphins.
In my experience the best walls I have dived were in Fiji - Noels and Yellow walls. Many fish, very healthy coral both hard and soft were there. It provided many more photo ops than I found in FP.
Both had current and surge. Fiji's was Somosomo straights and around the edges of islands. The exception was Noels and Yellow walls with nonexistent surge and slow current. FP obviously had currents in the passes and surge especially on the outsides of the fringe reef.
Things to do and night life near Taveuni (Matangi) were non-existent. Taveuni had Bouma Park and has three waterfalls with hiking. Trails can be very slippery. The main island, Viti Levu and Nadi, has much more to do - shopping, eating, night life, and most likely tours of some sort.
Most of the FP population is in Tahiti and most other islands we saw in the Society and Toumotus have little or no shopping on the scale you mentioned.
While Nadi and Papeete are larger and would have more non-diving things to do, it seems to me that neither is similar to Cozumel in terms of touristy things. Cozumel has far more cruise ship traffic and fortunately/unfortunately many businesses are geared to them. Thankfully in Fiji and FP, I did not see one balloon hat.
If you want to split things then maybe go to Fiji, Viti Levu and further out, maybe Taveuni or Vanua Levu for more peace and quiet. Or if FP then maybe stay on Tahiti and use the ferry to Moorea then go to Rangiroa and Fakarava. We generally found Fiji to be cheaper than FP.
I don't know of other locations where you will have lot's of big stuff and tons of fish for diving and the larger population for touristy things. You'll see more fish in Pacific sites than Caribbean locations and seems for you, is easier from the West coast.
Caribbean locations are becoming geared toward cruise ship traffic. As a dark horse you could look into Bonaire for fish and some island life, possibly some windward islands like Grenada, St. Lucia, etc. These will be more of a pain from the West coast. The only place I saw bigger stuff, sharks, was in the Bahamas.
If you haven't searched here on SB for trip reports, please do so. There will be more detail about topside and UW experience.
