There's nothing wrong with stranded wire, it just means if it's carrying voltage and a few strands snip or break (leading to greater than 15% voltage loss) it can cause issues. Solid is simply an all or nothing kind of wire. This is more of an issue though if you don't get every stand under the terminal, otherwise it can be beneficial due to the fact that there is plenty more "wire" to name contact with each other in case a stand breaks in some way along the middle or not at either end. (Bearing being crushed, chewed, or other thing where the wires no longer make any contact with the rest of the wire)

The only thing I use solid core for is fire alarm systems (where all or nothing is crucial), certain audio equipments, and anything nearing high voltage which a thermostat generally doesn't reach. If it does take 120v+ then wow what why.

Tinned tips though always help for sure, definitely makes it easier to remove/insert the wire.

Been a technician for the last 10 years now an thats my understanding of it atleast.