@Itchthescratch say that there was a period of 5 years during which the housing market is really sluggish and house price increases only just exactly matched inflation, rather than exceeding it.
Say person A and person B each have £400,000 to invest in year 1. Person A puts their £400,000 in a 5-year term cash investment product which guarantees an interest rate which will always match inflation (yeah I know there are inflation-beating options but this is to keep the maths simple) and Person B buys a £400,000 property in year 1 which they then sell after 5 years.
In the meantime, inflation is steady at 2.5% per year for 5 years.
Again for maths simplicity we'll say both A and B are higher rate taxpayers but not in the Addtional Rate band, and they've both maxed out their ISAs separately so that we don't need to fossick with ISA rules.
Person A's £400,000 investment earns £52,563 in compound interest across 5 years. The first £500 each year of savings interest is tax-free so they pay income tax at 40% on the rest so will pay a total of £20,025 in additional income tax on their investment income
Person B's £400,000 investment in a property also earns £52,563 in the difference between bought price and sold price, despite it being the same value in "real terms" as you put it. Under current rules the CGT they pay on that £52,563 is only 25% so they pay £13,140 in tax despite having had the same benefit from their investment compared to the cash investor.
If anything, CGT should be more, not less, but under the system you are proposing person B should pay zero tax on this part of their income because their investment "only" kept pace with inflation. Should the same be true for person A too?