For the most part, seems okay, but may be subject to change as more designs come out.
As of right now, I'll probably reserve Arcanine and the Eeveelution line (latter will probably require a different design strategy, given Eevee's unorthodox evolutions and all). For legendaries, calling the Eon siblings, but let's get to them after we flesh out the standard 'mons.
In this case, 2 stage 'mons may break the template a bit and fall under the guidelines I suggested earlier (i.e. Arcanine has higher BST comparatively, so potentially Level 6-7; Eeveelutions likely Level 6, but can try to make them Level 5).
We'll have to see, because yeah, the template isn't accurate for scaling as some 'mons are comparatively larger than the averages they're designed for. In terms of ideal BST limits, you can probably use these as rough guidelines.
- Stage 2: More/less referring to the middle stages for the 3-part ones; not for the entirety of fully-evolved 'mons like the ones that only evolve once.
- BST 380 - 450/460? (It's a iffy limit because some fully evolved stuff do have a lower BST than even mid-stage evolutions, though a few have abilities that double their stats)
- Fully-evolved: Normally the range is for 500-540 BST, but some smaller ones may need higher Levels to accommodate for their stronger attacks/defenses. Conversely, really gimmicky ones may be lower Level (like what you did with Magcargo)
- Arcanine has BST 555, which is technically the highest out of any non-Mega or legendary 'mon without drawbacks (Archeops and Slaking both have higher stats, but their abilities suck).
In a sense, setting absolute Level limits isn't exactly a good idea because exceptions do exist and can fall out of the ranges. Granted, a few 'mons who are in the BST range for fully-evolved mentioned above aren't exactly great except for walling due to absurdly high defenses (and HP) and bad offense, so they can fall into the Level 4 range. Others can probably fall into the specs in the template, but in a lot of cases, some design room may be needed.
Yeah, difficulty in designing Pokemon cards given the above are a reason why I only picked certain 'mons to design for, and not the entire Pokedex.
Legendaries (mythicals are grouped here too) and most of the competitively used stuff (roughly UU and above) are easier to categorize by Levels; the most obscure stuff in PU (or not having viable offenses, etc) and whatnot pose some challenge.