No, and believing this cuts you out of most of the market for no benefit. The rule is that no more than 100 passengers can be ashore at any one site at any one time. It caps how many people are standing on land, not how big your ship is allowed to be. Ships up to around 200 passengers handle it by splitting into groups and rotating, and you still get your time ashore.
Ships under 100 do have a real advantage: everyone can be ashore together, so the shore window is longer. Whether that's worth building your whole search around is another matter. Most guests are ready to head back to the ship after 60 to 90 minutes, and the extra time mainly pays off for serious photographers.
There also just aren't many of them. Fixating on sub 100 narrows you to a handful of expensive vessels and rules out ships that would suit you better on the things that actually shape your day.