As for Pokemon, I would say the non-third entries (Emerald, Platinum) are clearly not low-budget. Mid-budget at least.
A lot of the design work is in place from one game to the next yeah, and Game Freak is a relatively small dev house, but they typically spends years working on each new game (they have at least two teams working on two different games at any given time, allowing them to release every ~1.5 years nowadays.) They replace at least 2/3 of the sprite in every game, up to 100% in the new-generation games (even B/W which were on the same hardware! and they animated them as well.) The music is among the best on whatever platform the Pokemon game in question is on, and the attention to detail (both for noobs and hardcore players) is staggering. The inclusion of the Battle Tower/Frontier/Subway STILL blows my mind and combined with stuff like the egg tricks (Flame Body halves hatch times), vitamins, etc. clearly shows they cater to the hardcore EV grinder as much as the 7-year old kid with an all Pikachu team. The amount of work into appeasing both (especially the hardcores) and balancing just right isn't the mark of a low-budget game at all.
Comparing that to a game that uses art reinterpretations of characters that wouldn't be fit for DeviantArt and includes stuff like tapping out beats to pre-rendered PS1 FMVs is an affront to my sensibilities, personally.
"But it's fun!" Well, sure, but I wasn't arguing that. In fact I wasn't even comparing it with Pokemon, so I don't know how things veered off into that straw man. Comparing Theatrhythm to both of the 3DS's other notable rhythm games (Rhythm Thief R and now HarmoKnight), Square's entry definitively comes off as cheaper. Making matters worse is that Game Freak's is an eShop game and will probably be priced around 25% of Square's game.
That was the point I was making.