Strand tests only give a tiny snap shot of information. They are usually taken from the back, rarely from the front or hairline where hair is naturally weaker. Doing a strand test only gives a limited amount of information.
Colour build up from previous colours tends to happen and stick more on the hair at your hairline and nape. The finer hair.
The good news is, your hair will eventually regain the curl. It's going to take a while though. If your hair has been damaged it will affect it's natural texture, causing hair to become frizzier, rougher, elastic, limp, loss of density, and broken. It can be one of those or a mixture depending on the level of erosion to the cuticle and the cortex.
Aftercare:
Before washing or bed, brush gently with a tangle teezer or wet brush.
2 x shampoos using either olaplex 4 or a protein based shampoo like kerastase bain de force architecte.
Gentle towel dry for best results or squeeze out all excess water. Apply conditioner from root to tip (yes, really - because of the damage) use olaplex 4 or kerastase ciment anti usure leave for a min of 3 mins. Detangle with conditioner in using a wet brush or tangle teezer. Rinse throughly
Pat dry hair DO NOT WIND TOWEL AROUND WET HAIR OR FLUFF/RUB TOWEL to dry.
Use a protein based masque like the one you've mentioned. Use it in place of the conditioner or olplex Step 3. Once per week. Leave for 10 mins.
Before drying or combing, brushing wet hair apply a leave on treatment or heat protection, then comb. This will help to minimise traction breakage. Heat protections to use to balance the protein should be moisture based or a combination of protein and moisture. Redken 21 benefits or kerastase nectar thermique are ideal for this.
Style as usual. Do not put your hair up while it's still wet, it will cause more breakage. Only use hair ties when it is fully dried.
Blow dry or diffuse, you can use your normal styling products over the heat protection. Minimise the use of other hot tools.
Get your hair cut and toned again, have an in salon treatment or bonding treatment every 6 weeks. This will help help splits and breaks from worsening over time and will help blunt off anything.
If you can afford to and if the level of damage is severe I would recommend in salon treatments every 2 weeks for the next 8-12 weeks. Your hair will need both protein and moisture to recover.
I would definitely being going back to the original stylist after getting a second opinion. The salon should offer you treatments free of charge or some hair care products to help. This naturally depends on the level of damage sustained and what was said and then carried out during your appointment. Any self-respecting salon or stylist should/would want to help with this. It's in their best interest to maintain and secure a relationship with you as a client.
It's very hard to advise without seeing your hair but hopefully there's enough information here to help empower you and start on the recovery process.
If you have any other questions, I'm happy to help.