It depends on the type of development work you'll be working in. The main role of a Solutions Engineer is to translate marketing vision into technical specs. Take note on the word "vision", it means the customer will have high expectations because usually marketing/sales will present your product like it can do everything. Solutions Engineers mainly deal with high-touch sales, only means one thing: large enterprise customers.
If the customers you'll be handling would be up in AWS/Google, it's good, but if they have on-premise, that means you'll really have to know your stuff about the following:
- Feature Lists - translating what the product does into a feature list that describes perfectly what the customers are looking for. Makes it easier for them to explain to the board so they can get budget and approach finance and procurement.
- Active Directory or Auth0 integrations
- Network - from DNS/dnsmasq to iptables
- VA stuff - meeting generic hardening requirements and VA scans, java key stores, SSL certificates/ciphers and ton of Linux/Unix or Powershell.
- Linux/Unix - NTP, mail servers if need be, proxying using nginx/apache, user access, etc.
- Architecture - explaining the entire product in high-level and how components integrate with a customers current infrastructure
- Benchmarking - customers will ask apples to apples comparisons with other vendors, and they'll stick by your numbers.
- Appliance/Infrastructure sizing - you'll probably take part by this. Certain customers will definitely ask data growth and network growth as well. They need this to line up corporate budget.
and a lot more
So being a web developer is just a piece of the pie. Full stack is a must.