Yes, it is argued that Axolotl is stronger than Bill because Bill begged Axolotl to save him, but there are several flaws in this argument:
Bill was begging Axolotl to save him because his powers were gone; he was not begging for Axolotl as a higher power, who is come and save him. To put it in simple terms, let's say there is character X, and character X is stronger than character B, but after character X's powers are gone, character X is dependent on character B, who was weaker than him in the past, to save his life. More than that, Bill himself sees Axolotl as a copilot (The points to consider here are that these statements are written by Bill's Symbol Substitution Cipher).
Furthermore, if Bill gains a physical form, it is stated that he will become so powerful that even Time Baby and Axolotl (The Big Frilly) will be unable to stop him, and while Bill is usually a rather egotistical character, but if he encounters a character as powerful as he is, he will make it quite clear that he is influenced by that character (Like Bill being impressed by Dipper, Mabel, and Soos when he was defeated by them in Mindspace and admitting that he was marginally stronger than Time Baby when he was not in his physical form). It's also made quite clear in the series that if Bill gains a physical form, it's all over (According to the data from Journal 3, it seems that Ford knew about Axolotl.)
If we talk about Axolotl's power level, Axolotl would probably be at a similar level to Time Baby because he was probably associated with Time Baby, who was close to Bill in terms of power before he got his physical form. Also, I don't know how helpful it is, but Axolotl exists in "time and space between time and space," but that probably doesn't give it any rank. In short, he should be on the same level as Time Baby, who is scales to Pre-Physical From Bill Cipher, who is would be can tamper with alternate realities.
Bill also needs to have a new key named "Pre-Physical Form" with a Low 2-C. Also, Bill Cipher's "Full Power" key should be renamed "Post-Physical Form."
Extras:
These scans can also be used to support Time Baby's level.
Axolotl should be has Light Manipulation: Made its eyes glow when answering Dipper.