I have a new born panpore and are wondering is it is worth training hard, since it is hard to level up after a while.
In my honest opinion, yes they are a lost cause. Unidentified and Shxatoap are correct in saying that they have a possbility of being good at the lower/beginning part of gameplay, but I had one on my first playthrough (didn't like my starter so I restarted after 3rd badge) and I used Panpour. It was seriously ridiculous on how bad this thing would get owned. I got dropped by level 7-10 Patrats in like one or two hits. If you want to stick it out and give them a shot then by all means give it a shot, but as far as I'm concerned if they are better at the beginning of the game or lower tier, why not wait until a cool/strong water/fire/grass type comes a long and train it. No need to train multiple Pokemon of one certain type until the end game. Hope this helps.
The elemental monkeys are good in lower Tiers,since their better version (Like Sceptile for Simisage and Infernape for Simisear) are in the higher tiers. They are good with Sub-Berry Strategies since both of their abilities (Gluttony and Blaze/Torrent/Overgorw) are great with that Strategy. Plus they have Nasty Plot which is a huge asset. And they are versatile,they can be Physical,Special or Mixed with Work Up.
I noticed that they were quite weak as combat pokemon as well. Looking deeper into their movesets, they strike me as supportive pokemon, rather than direct combat ones. Incinerate to kill berries, Scald for the Burn, Leech Seed...
Double, Triple, or Rotation battles are where they belong, not in normal 1v1's.